^IOS  ANGELA 


,vlOS-ANCElf 


i  I 


i  i 


8     2 

s  I 


I    S 


clOSANCElfj> 


^OF-CAIIFO%          <\\\EUNIVER£/A 

i  l^r\t    ^o<r^  s 

t, 


3 


^clOS-ANCEU^ 


0x,       .-SJ&H1BRARY0X 


^AHvuaiH^' 

\\\E-UNIVERS/^         ^-lO  ' 


lV£)l  I 


PRACTICAL    COLOR 
PHOTOGRAPHY 


BY 

E.  J.  WALL,  F.C.S.,  F.R.P.S. 

Author  of 

"The  Dictionary  of  Photography," 
"  Carbon  Printing,"  etc. 


SOUTHERN 


AMERICAN  PHOTOGRAPHIC  PUBLISHING  CO. 

BOSTON  17,  MASSACHUSETTS 

1922 

49362 


COPYRIGHT,  1922,  BY 

AMERICAN  PHOTOGRAPHIC 

PUBLISHING  CO. 

Entered  at  Stationers'  Hall 

PRINTED    IN    THE    UNITED    STATES    OF    AMERICA 

Electrotyped  and  printed,  June,  1922 


THE   PLIMPTON   PRESS 
NORWOOD,  MASS.  U.S.A. 


I 


PREFACE 

N  this  little  work  historical  and  theoretical  data  have 
-  been  as  far  as  possible  omitted.    My  endeavor  has 
been  to  supply  an  elementary  practical  manual  of  the 
,.X        various  processes  of  Color  Photography,  and  no  method 
or  formula  has  been  given  that  has  not  been  personally 
tested  in  practice.    This  has  naturally  limited  the  scope 
S  of  the  work  to  some  extent,  but  it  has  not  entailed  the 

omission  of  any  information  of  practical  value. 

E.  J.  WALL. 
Wollaston,  Mass.,  May,   1922 


(•• '     '  "' 

j         SO 


CONTENTS 

CHAPTER  I.    The  Spectrum  —  Color  Formation i 

CHAPTER  II.    The  Sensitive  Plates  — How  to  Prepare  Them 

—How  to  Back  Them  —  Commercial  Plates 12 

CHAPTER  III.  Color  Filters  —  Breaking  Up  the  Spectrum  — 
Additive  and  Subtractive  Filters  —  How  to  Make  Filters 

—  Commercial    Filters  —  How    to    Cement    Filters  — 
Mounting  and  Using  Filters 22 

CHAPTER  IV.  The  Darkroom  —  Safelights  —  How  to  Make 
Them  —  Desensitizing  Plates  for  Development  in  Bright 
Light  —  Developers  and  Development — Fixing  and 
Washing 41 

CHAPTER  V.  The  Camera  and  Exposure  —  Construction  of  a 
Single-exposure,  Three-image  Camera  —  Lenses  —  Ex- 
posures—  Filter  Ratios  —  Marking  the  Separation  Nega- 
tives for  Later  Identification 50 

CHAPTER  VI.  Subtractive  Processes  —  Superimposed  Carbon 
Prints  —  Theory  of  Carbon  Printing  —  Sensitizing  the 
Tissues — Printing  —  Development — Transfer  to  Final 
Support  in  Superposition  —  Cementing  —  The  Raydex 
Process 60 

CHAPTER  VII.  The  Imbibition  Process  —  Pinatype  —  How 
to  Make  the  Printing  Plates  —  Sensitizing — Printing 

—  Staining — Pulling  the  Images  —  Registration  —  Im- 
proving Imperfect  Results 75 

CHAPTER  VIII.  Relief  Processes  —  The  Positive  —  Bleach- 
ing—  Staining  and  Printing  —  The  Etching  Process  — 
The.  Negatives  —  Etching,  Staining  and  Printing  — 
Developed  Relief  Processes  —  Working  Details 84 


vi  CONTENTS 

CHAPTER  IX.  Mordanting  and  Toning  Processes  —  The 
Diachrome  Process  —  Manipulation  —  Dyes  and  Staining 

—  The   Copper   Mordanting   Process  —  The   Vanadium 
Mordanting  Process — The  Chemical  Toning  Process  — 
The  Combination  of  Processes 95 

CHAPTER  X.  The  Three-color  Gum-bichromate  Process  — 
Treatment  of  the  Paper  —  Preparing  the  Coating  — 
Pigments  —  Coating  the  Paper  —  Exposure,  Develop- 
ment and  Recoating  —  Registration no 

CHAPTER  XI.    Three-color  Lantern  Slides  —  Use  of  Celluloid 
Film  —  Making  the  Emulsion  —  Sensitizing  —  Printing  — 
Staining  —  Pinatype  Slides  —  Assembling  —  The  Photo- 
chromoscope 117 

CHAPTER  XII.  Screen  Plates  —  History  —  Theory — Sepa- 
rate and  Combined  Methods  —  The  Compensating  Fil- 
ter—Position of  the  Film  —  How  to  Make  the  Filters 

—  Flashlights  and  Appropriate  Filters  —  Exposure  of  the 
Screen  Plates  —  Meters  —  Development  —  Desensitizing 

—  Reversal  of  the  Image  —  The  Second  Development  — 
Intensification  —  Fixation    and    Drying  —  Varnishing  — 
Artificial   Light  Work  —  Failures  and   Remedies  —  Ex- 
hibiting    Screen     Plates  —  Projection  —  Printing     from 
Screen     Plates  —  Filters     and     Manipulation  —  Mathe- 
matics of  Necessary  Distances  —  Stereoscopic  Work  with 
Screen  Plates 136 

CHAPTER  XIII.    The   Bleach-out  Process  —  Fugitive  Dyes 

—  Preparation    of    Sensitive    Material  —  Printing   and 
Fixing 179 

CHAPTER  XTV.  The  Lippmann  Process  or  Interference  Helio- 
chromy —  History  —  Theory  —  The  Nature  of  Light  — 
Interference  Phenomena  —  Preparing  the  Sensitive  Film 

—  Sensitizing  for  Color— The    Plateholder  —  Exposure 

—  Development  and  Fixing  —Viewing  the  Colors  ....    185 

CHAPTER  XV.  The  Seebeck  Process,  or  Photography  with 
Silver  Subchlorides  —  Another  Laboratory  Process  — 
History  —  Making  the  Paper  —  Printing 200 


CONTENTS  vii 

-  CHAPTER  XVI.  The  Diffraction  Process  —  Diffraction  Grat- 
ings —  Making  the  Plates  —  Printing  —  Viewing  —  Re- 
production    205 

CHAPTER  XVII.    The  Prismatic  Dispersion  Process  —  Con- 
struction  of  Apparatus  —  Operations 212 

-  CHAPTER  XVIII.  Two-color  Processes,  Bi-packs  and  Tri- 
packs  —  Discussion  of  Definition  —  Methods,  Adjust- 
ments and  Operative  Details  — Kodachrome 217 

CHAPTER  XIX.    Cinematography  in  Colors  —  History  and 

Difficulties — Proposed   Methods  —  Future   Possibilities.     230 

CONVERSION  OF  WEIGHTS  AND  MEASURES 235 

BIBLIOGRAPHY 238 

POSSIBLE  SOURCES  OF  VARIOUS  DYES 241 

INDEX 243 


PRACTICAL 
COLOR    PHOTOGRAPHY 


CHAPTER  I 
THE  SPECTRUM  —  COLOR  FORMATION 

BEFORE  considering  the  various  processes  of  color 
photography,  it  is  essential  to  explain  the  formation 
of  color,  and  the  difference  between  the  additive  and  sub- 
tractive  methods  of  color  reproduction. 

The  source  of  all  color  is  the  spectrum  or  ribbon  of 
colors  formed  by  the  dispersion  of  white  light.  When  a 
narrow  slice  of  white  light  is  passed  through  a  prism,  it 
is  spread  out  into  a  band  of  various  colors,  ranging  from 


[           < 

>                         F           fc     1 

I 

\ 

L 

-L            J.       _1_ 

_L 

T 

J 

FIG.  i 

red  through  orange,  yellow,  green  and  blue  to  violet. 
This  is  nothing  more  than  an  artificially  made  rainbow, 
and  while  the  colors  enumerated  above  are  the  principal 
ones,  they  insensibly  merge  one  into  the  other  so  that 
there  are  innumerable  intermediate  tints. 

In  Fig.  i  is  shown  a  normal  spectrum,  giving  approxi- 
mately the  distribution  of  the  colors.  It  will  be  seen 
that  there  are  numerous  transverse  lines,  designated  by 


2  COLOR  PHOTOGRAPHY 

the  letters  of  the  alphabet,  which  always  occur  in  the 
same  places,  that  is  to  say  in  the  same  color  regions,  no 
matter  what  the  method  of  spectrum  production  may  be, 
for  there  are  other  ways  of  forming  spectra  besides  the 
use  of  a  prism,  such  as  by  means  of  diffraction  gratings. 
These  lines  are  called  the  Fraunhofer  lines,  from  the 
physicist  who  first  mapped  them  out,  and  who  assigned 
to  them  the  letters  by  which  they  are  known.  They 
may  be  looked  upon  as  convenient  milestones  or  data 
posts,  which  enable  us  to  identify  any  color  at  once. 
For  instance,  the  E  line  occurs  in  the  middle  of  the  green 
and  if  we  were  to  designate  the  color  of  a  dress  material 
or  a  dye  as  similar  in  color  or  hue  to  the  E  line,  there 
would  be  no  question  as  to  its  exact  shade;  whereas  the 
mere  term  "green"  conveys  no  definite  meaning.  It  is 
very  common  practice  to  define  a  position  in  the  spec- 
trum with  regard  to  these  lines,  and  we  may  meet  with 
such  terms  as  B  \  C  or  E  f  F,  which  also  define  the  color, 
as  one  has  merely  to  locate  these  particular  points  to 
determine  at  once  the  particular  color  designated. 

All  natural  objects  possess  the  property  of  absorbing 
more  or  less  of  white  light  and  reflecting  the  remainder, 
and  to  this  property  their  characteristic  colors  are  due. 
The  absorption  may  be  general  and  equal  for  every  part 
of  the  spectrum,  when  we  obtain  light  of  lowered  luminos- 
ity or  brightness  which  is  called  grey.  If  the  absorption 
is  complete,  then  obviously  we  have  a  total  suppression 
of  all  color  and  light  and  the  resultant  is  black.  But  if 
one  region  of  the  spectrum  is  absorbed  more  than  an- 
other, that  is  to  say,  if  the  object  selectively  absorbs 
part  of  the  spectrum,  the  sum  of  what  is  left  is  color. 

A  concrete  example  of  the  selective  and  absorptive 
power  of  objects  is  afforded  by  a  very  simple  experiment. 


THE  SPECTRUM  —  COLOR  FORMATION      3 

Nearly  fill  a  black  vulcanite  dish,  such  as  is  used  for 
developing,  with  a  solution  of  ammonio-sulphate  of  cop- 
per, which  can  be  made  by  dissolving  cupric  sulphate  hi 
distilled  water  (about  a  ten  per  cent  solution  will  do), 
and  adding  strong  ammonia  until  the  whitish  precipitate 
which  is  formed  at  first  is  redissolved.  A  very  rich  blue 
solution  is  formed,  and  if  this  is  poured  into  the  dish  to 
the  depth  of  about  three-quarters  of  an  inch,  it  will  ap- 
pear quite  black.  But  if  a  sheet  of  opal  glass  or  white 
cardboard  is  placed  in  the  solution  at  an  angle,  so  that 
one  end  rests  on  the  edge  of  the  dish  and  the  other  on 
the  bottom,  it  will  be  seen  that  the  solution  is  actually 
colored  and  that  the  color  shades  off  from  the  white  of 
the  opal  glass  through  all  shades  of  blue  to  almost  black 
at  the  other  end.  This  experiment  proves  in  the  first 
place  that  there  must  be  some  reflective  surface  capable 
of  sending  back  to  our  eyes  the  incident  light,  and  in  the 
second  place  it  also  shows  that  the  thicker  the  stratum  of 
colored  substance  the  deeper  the  color.  In  the  case  in 
point,  the  white  light  incident  on  the  liquid  penetrates 
to  some  depth,  and,  without  the  opal  glass,  reaches  the 
black  surface  of  the  tray.  As  this  reflects  no  light,  the 
solution  appears  black;  but  on  the  insertion  of  the  glass 
the  incident  light  meets  its  surface,  which  reflects  the 
whole  of  the  light,  except  that  absorbed  or  suppressed  by 
the  liquid.  It  is  obvious  that  the  light  actually  traverses 
a  double  thickness  of  the  solution  at  any  point,  first 
through  one  distance  to  the  glass  and  then  through  the 
same  thickness  to  the  surface  again,  so  that  the  depth  or 
intensity  of  color  is  due  to  a  double  absorption. 

The  processes  involved  in  the  above  experiment  are 
continually  taking  place  with  all  objects.  Light  pene- 
trates below  their  surfaces  to  a  greater  or  less  depth,  and 


4  COLOR  PHOTOGRAPHY 

meets  a  reflective  layer;  if  the  substance  possesses  selec- 
tive absorption,  then  the  reflected  light  is  colored. 

The  absorption  or  suppression  of  a  particular  spectral 
region  gives  color,  and  this  is  roughly  shown  in  the  ac- 
companying diagram,  Fig.  2.  It  will  be  seen  that  with 
the  exception  of  green,  all  the  colors  are  due  to  the  sup- 
pression of  one  region  only,  while  in  this  case  there  are 
two  absorption  bands,  one  at  each  end  of  the  spectrum. 


FIG.  2 

On  the  left  of  the  above  diagram  is  given  the  color 
that  is  absorbed  and  on  the  right  the  residual  color.  It 
will  at  once  be  seen  that  while  we  are  accustomed  to 
talk  of  yellows,  blues,  crimsons,  etc.,  these  are  not  simple 
colors,  but  the  sum  of  those  spectral  regions  that  are 
left  when  a  certain  band  is  cut  out.  It  is  also  evident 
that  if  the  right  and  left  hand  colors  be  added  together 
the  result  must  be  white  light,  because  we  are  merely 


THE  SPECTRUM  —  COLOR  FORMATION      5 

restoring  that  which  was  temporarily  removed.  Two 
such  colors,  which,  when  mixed  together,  form  white 
light,  are  said  to  be  complementary  colors.  There  are 
innumerable  possible  pah's  of  complementary  colors,  for 
it  may  be  said  that  with  the  exception  of  the  greens 
every  line  or  point  in  the  spectrum  has  its  complemen- 
tary. In  the  case  of  green  the  real  complementary  lies 
outside  the  spectrum,  and  can  only  be  matched  by 
assuming  that  instead  of  the  spectrum  being  a  straight 
line,  it  is  actually  a  circle  with  the  red  and  violet  over- 
lapping, forming  the  magentas  or  crimsons,  in  which  lie 
the  complementaries  to  green. 

If  we  take  two  of  the  complementaries  shown  above, 
number  II,  in  which  blue  is  suppressed,  with  yellow  as 
the  resultant  color,  and  number  VI,  which  is  violet-blue, 
and  if  we  assume  that  we  can  match  these  in  pigments 
with  lemon  chrome  and  ultramarine,  and  mix  these  pig- 
ments together,  we  shall  find  that  we  obtain,  not  white, 
but  a  more  or  less  dirty  olive-green.  This  seeming  para- 
dox leads  us  to  another  fundamental  fact,  which  is  that 
an  admixture  of  pigments  does  not  give  the  same  results 
as  an  admixture  of  lights.  Although  this  is  a  much  mis- 
understood subject  it  is  really  very  simple,  but  we  will 
defer  the  complete  explanation  till  we  have  cleared  a 
little  more  ground. 

The  length  and  breadth  of  the  spectrum  are,  like  a 
camera  image,  dependent  entirely  on  the  instruments 
used.  Everybody  knows  that  the  picture  made  with  a 
vest-pocket  camera  may  include  as  much  of  a  given  sub- 
ject as  a  10  x  12  print;  the  size  of  the  result  is  deter- 
mined by  the  focal  length  of  the  lens  and  the  size  of  the 
plate  or  film,  and  is  not  dependent  on  the  subject.  It 
is  obvious  that  if  we  ignore  for  the  time  being  the  Fraun- 


6  COLOR  PHOTOGRAPHY 

hofer  lines  and  divide  our  spectrum  from  the  violet  to 
the  red  end  into  equal  steps,  starting  with  wave  length 
4000  for  the  former  and  limiting  the  red  to  7000,  then  we 
have  3000  different  measurable  steps  which  actually 
differ  one  from  the  other  in  color.  Although  our  eyes 
are  not  sufficiently  sensitive  to  differentiate  between 
such  fine  gradations,  yet  they  are  capable  of  recognizing 
a  great  many,  about  128  in  all.  This  being  the  case,  the 
question  arises  as  to  how  we  become  conscious  of  color. 
Have  we,  as  it  were,  128  strings  or  wires  in  our  eyes, 
each  of  which  responds  to  one  of  these  small  spectrum 
steps,  or  is  there  some  simpler  system?  Apparently  the 
system  that  answers  all  theoretical  requirements  is  a 
three-wire  one.  It  has  been  established,  principally  by 
the  researches  of  Young  and  Helmholtz,  that  we  have 
but  three  nerve  fibrils  in  the  retina,  the  sensitive  surface 
of  the  eye,  which  respond  to  all  the  colors  of  the  spec- 
trum. By  the  simultaneous  and  equal  excitation  of  these 
three  nerve  fibrils  we  receive  the  sensation  of  white,  and 
those  of  other  colors  by  the  action  of  two  of  them. 

We  may,  therefore,  say  that  there  are  three  fundamen- 
tal or  primary  colors  in  the  spectrum,  by  the  admixture 
of  which  we  can  form  all  intermediate  colors  and  white. 
The  positions  of  these  fundamental  colors  are  shown  by  the 
heavy  vertical  lines  R.  G.  B,,  in  Fig.  3,  and  the  curves 
show  how  the  intermediate  colors  are  formed.  It  will 
be  seen  from  the  diagram  that  the  fundamental  red  is 
at  about  6700,  and  this  excites  but  the  one  sensation; 
but  the  green  at  5180  not  only  excites  the  green-sensitive 
nerve  fibril  but  also  the  red  and  the  blue,  while  the  blue 
at  4600  excites  the  green  and  red  also,  though  but 
slightly.  If  we  now  take  any  intermediate  color,  such 
as  orange  at  6000,  we  only  have  to  draw  a  vertical  line 


THE    SPECTRUM  —  COLOR    FORMATION     7 

through  this  point;  the  distances  at  which  this  cuts  the 
two  curves  R  and  G  give  the  relative  amounts  of  red  and 
green  light  required  to  match  this  particular  color,  and, 
as  will  be  seen,  this  is  about  70  red  plus  35  green. 
There  is  another  and  very  striking  experiment,  which  can 
be  performed  by  the  aid  of  three  projection  lanterns;  if 
these  are  arranged  to  throw  three  superimposed  circles, 


S50 

FIG.  3 

the  correctly  colored  red,  green  and  blue-violet  niters 
placed  in  them,  and  the  three  objectives  fitted  with  iris 
diaphragms,  it  is  easy  to  show  every  color  of  the  spec- 
trum. For  instance,  if  we  project  the  red  disc,  and  cap 
the  green  and  blue  lenses,  we  have  the  fundamental  red 
color  sensation;  now,  after  closing  the  diaphragm  of  the 
green  lens  to  its  smallest  aperture,  we  can  gradually  mix 
green  light  with  the  red  by  slowly  opening  the  green  dia- 


8  COLOR  PHOTOGRAPHY 

phragm,  when  the  red  light  on  the  screen  will  be  seen  to 
turn  gradually  more  and  more  orange,  until,  when  both 
lenses  are  at  full  aperture,  we  have  practically  a  pure 
yellow.  Now,  by  gradually  closing  the  iris  of  the  red 
lens,  the  light  will  become  first  yellowish-green,  then 
greenish-yellow,  and  finally,  when  the  red  is  completely 
cut  off,  pure  green  of  the  fundamental  hue.  In  exactly 
the  same  way,  by  manipulating  the  blue  lens  diaphragm, 
we  can  show  the  gradual  transition  of  the  pure  green 
through  all  the  intermediate  shades  of  greenish-blue  and 
blue-green  to  pure  blue.  By  manipulating  the  green 
diaphragm  we  can  show  the  transition  from  pure  blue  to 
the  fundamental  blue-violet,  which,  for  the  sake  of 
brevity,  is  generally  called  blue.  By  mixing  with  this 
the  red,  we  can  run  through  the  whole  gamut  of  crim- 
sons, magentas,  pinks  or  purples,  for  all  these  terms  are 
used  indiscriminately  to  designate  these  colors.  Finally, 
if  all  three  lenses  are  working  at  their  full  aperture,  we 
obtain  white,  assuming  that  all  three  light-sources  are 
of  equal  intensity;  if  this  is  not  so,  the  white  obtained 
will  be  more  or  less  tinged  with  color,  which  may  require 
slight  adjustment  of  one  or  another  of  the  diaphragms. 

We  have  here  the  addition  of  light  to  light,  for  we  start 
out  with  a  black  screen,  that  is  one  without  illumination, 
project  red  light  on  it,  then  add  the  green  and  the  blue- 
violet,  with  the  final  product  of  a  white  screen.  It  will 
now  be  easy  to  understand  how  we  can  show  a  picture 
in  colors.  Let  us  take  the  very  simplest  example,  such 
as  pieces  of  glass  with  opaque  lantern-slide  binding  strips 
pasted  thereon  at  different  angles,  and  we  can  at  once 
grasp  the  formation  of  the  final  colored  pattern.  Assum- 
ing that  we  have  a  white  circular  disc  illuminated  by  the 
respective  fundamental  colors,  we  place  in  the  red  Ian- 


THE  SPECTRUM  —  COLOR  FORMATION      9 

tern  a  sheet  of  glass  with  a  vertical  stripe  of  opaque 
material.  Obviously  this  shuts  out  the  red  light,  so  that 
we  have  a  result  such  as  shown  in  Fig.  4.  At  the  sides 
all  three  lights  are  present  and  give  us  white;  in  the 
vertical  stripe  the  red  is  cut  out,  only  the  green  and 
blue-violet  being  present,  therefore  the  result  is  a  pure 
blue  stripe  on  a  white  ground.  Now  let  us  insert  in  the 
green  lantern  an  opaque  cross  with  the  arms  at  an  angle 


FIG.  4 

of  45°  to  the  vertical  stripe;  then,  the  green  being  cut 
out,  the  result  is  a  mixture  of  the  red  and  the  blue- 
violet,  which  as  we  have  seen  is  crimson  or  pink.  In  the 
center,  where  the  image  of  the  cross  passes  over  the  ver- 
tical stripe  both  the  red  and  green  are  cut  off  and  only  the 
blue-violet  shows.  If  we  now  insert  a  glass  with  a  hori- 
zontal opaque  stripe  in  the  blue-violet  lantern,  where  this 


I0  COLOR  PHOTOGRAPHY 

cuts  out  this  color  we  have  the  admixture  of  the  red  and 
green,  that  is,  yellow,  and  in  the  center  where  all  three 
strips  cross  one  another  all  light  is  cut  off  and  we  have 
black.  The  final  picture  is  a  white  ground  with  a  blue 
vertical  stripe,  a  yellow  horizontal  stripe  and  a  crimson 
cross  with  a  black  center.  If  instead  of  using  opaque 
strips  we  use  lantern  slides,  which  range  in  opacities  from 
clear  glass  to  complete  blackness,  and  place  one  in  each 
lantern,  we  shall  so  cut  out  the  respective  lights  as  to 
give  us  innumerable  tints  and  shades  of  color  as  well  as 
greys  and  blacks,  and  as  the  silver  image  gives  the  forms 
of  the  objects  we  have  a  picture  in  its  natural  colors. 
This  is  the  theory  of  the  additive  process. 

It  is  not  always  convenient  to  use  a  lantern  or  an  in- 
strument in  which  the  three  images  can  thus  be  seen, 
and  we  naturally  desire  to  see  the  results  on  paper.  We 
have  then  another  proposition,  but  one  which  can  be 
explained  similarly.  We  start  in  this  case  with  an 
illuminated  white  surface,  and  if  we  place  a  coating  of 
red  pigment,  such  as  carmine,  on  this,  the  whole  sur- 
face will  be  red.  If  a  green  pigment  be  now  washed 
over  the  red,  the  color  becomes  a  dirty  indefinite  shade, 
which  might  be  called  olive-brown;  and  if  we  use  over 
this  a  blue-violet  wash,  the  result  will  be  black.  It  is 
obvious  that  our  fundamental  colors  as  used  for  the 
additive  process  are  quite  unsuitable  for  paper  prints. 
But  if  on  top  of  the  red  wash  we  place  a  yellow  one,  we 
obtain  a  more  or  less  pure  orange,  and  if  we  superimpose 
blue,  not  blue-violet,  we  shall  obtain  black,  because  the 
blue  absorbs  the  orange  made  by  the  red  and  yellow.  Blue 
on  top  of  yellow  gives  us  a  more  or  less  pure  green,  and 
in  conjunction  with  red  it  gives  us  the  crimsons.  There- 
fore, the  printing  colors  are  red,  yellow  and  blue. 


SPECTRUM  —  COLOR  FORMATION     n 


*MT  The  action  of  the  individual  colors  ought  to  be  clear 
(V/rrom  Fig.  2,  but  we  can  deal  with  it  in  another  way. 
Let  A  (Fig.  5)  represent  the  spectrum  reflected  from  a 
red  pigment,  and  B  that  of  a  yellow  pigment:  then  if 
these  spectra  are  superimposed  the  only  colors  reflected 
are  shown  in  C  from  D  f  E  to  the  red,  and  the  sum  of 


Red 


Yellow 


Orange 


Blue 


Yellow 


Green 


FIG.  5 

these  is  orange.  In  the  formation  of  greens  we  have  a 
similar  case:  let  D  represent  the  absorption  of  a  blue 
pigment,  and  E  that  of  a  yellow,  then,  superimposing 
these,  the  only  light  common  to  both  is  the  green  shown 
in  F, 

From  what  has  been  said  it  should  be  clear  that  we 
obtain  our  colors  in  the  case  of  prints,  and  lantern  slides 
as  well  when  they  are  colored  with  pigments,  by  sub- 
tracting colors  from  white  light;  therefore  this  process  is 
generally  known  as  the  subtractive  process. 


CHAPTER  II 
THE  SENSITIVE  PLATES 

EVERY  photographer  knows  that  the  ordinary  plate 
is  practically  color-blind,  that  is  to  say,  it  repro- 
duces the  violets  and  blues  more  or  less  like  white,  and 
the  greens,  yellows  and  reds  more  or  less  dark  or  black. 
As  in  color  photography  we  have  to  reproduce  reds, 
greens  and  blues  as  of  equal  value,  the  plates  used  must 
be  sensitive  to  these  colors;  therefore,  we  must  use  the 
so-called  panchromatic  plate.  Any  plate  can  be  color- 
sensitized  by  bathing  for  a  short  time  in  certain  dye 
solutions.  While  this  is  not  a  difficult  operation  and  the 
resultant  plates  actually  have  a  higher  color-sensitiveness 
than  commercial  plates,  which  are  made  by  the  addition 
of  the  dye  to  the  emulsion  just  before  coating,  it  is  not 
a  process  that  can  be  recommended  for  the  average 
worker.  In  the  first  place,  the  necessary  dyes  are  very 
costly,  and  must  be  purchased  in  commercial  quantities 
sufficient  for  a  great  many  plates,  although  actually  only 
a  very  small  quantity  is  used;  secondly,  efficient  drying 
arrangements  must  be  installed;  thirdly,  control  of  re- 
sults is  extremely  difficult,  in  consequence  of  the  many 
factors  involved;  fourthly,  bathed  plates  have  not  such 
a  long  life  as  commercial  plates;  lastly,  sensitizing  of 
plates  can  not  be  carried  on  successfully  in  a  room  that 
has  been  used  for  developing  and  fixing.  The  author's 
advice  to  beginners  in  color  work  is  to  adopt  commercial 
panchromatic  plates;  quite  enough  troubles  and  failures 


THE  SENSITIVE  PLATES  13 

will  be  met  with  in  the  ordinary  manipulations  without 
adding  extra  worries  about  the  sensitive  media. 

If  it  is  desired  to  experiment  in  this  field,  the  following 
instructions  will  be  helpful.  In  the  first  place,  it  is  not 
advisable  to  select  the  fastest  plates,  as  they  have,  as  a 
rule,  a  greater  tendency  to  fog  than  slower  ones,  and  this 
tendency  is  always  increased  by  bathing,  particularly  if 
the  plates  are  to  be  kept  some  time.  It  is  not  advisable 
to  bathe  less  than  a  dozen  plates  at  a  time.  A  medium 
plate,  normally  clean-working,  should  be  chosen.  Before 
entering  upon  the  actual  bathing  process,  it  may  be  as 
well  to  point  out  that  as  the  plates  are  rendered  sensitive 
to  red  it  is  not  advisable  to  use  red  light  for  the  dark- 
room illumination.  It  can  be  used,  but  as  one  can  see  far 
better  with  a  green  light  of  equal  power  it  is  preferable 
to  use  one  of  those  described  later  on  ( See  P.  41 ). 
But  the  plates  should  not  be  unduly  exposed  even  to  one 
of  these,  and  with  a  little  experience  it  is  astonishing  how 
easy  it  becomes  to  work  in  total  darkness,  just  switching 
on  the  green  light  as  required. 

While  grooved  troughs  are  the  most  convenient  for 
bathing  a  dozen  plates,  they  are  very  wasteful  of  solu- 
tion, and  so  flat  dishes  should  be  used.  If  one  suffi- 
ciently large  to  hold  four  plates  at  once  be  employed,  it 
is  almost  as  easy  as  using  a  trough.  An  interval  timer, 
clock  or  watch,  is  an  absolute  essential.  A  grooved 
trough  is  preferable  for  washing.  There  is  one  extremely 
important  detail,  on  which  the  author  lays  great  stress, 
and  that  is  that  the  dish  used  for  sensitizing  should  have 
been  used  for  no  other  photographic  operation  and  should 
be  kept  for  this  sole  purpose,  particularly  if  of  earthenware, 
as  this  soon  acquires  surface  cracks  into  which  the  devel- 
oping and  fixing  solutions  enter,  so  that  minute  traces 


I4  COLOR  PHOTOGRAPHY 

of  these  are  extracted  by  the  dye  solutions  and  all  sorts 
of  curious  markings  and  fog  may  be  the  result.  Glass 
vessels  are  preferable  to  all  others  and  they  should  be  of 
the  deep  variety.  In  no  case  must  metal  dishes  be  used 
for  sensitizing,  as  there  seems  to  be  some  peculiar  action 
that  results  in  the  formation  of  a  characteristic  coarse- 
grained fog,  which  increases  somewhat  rapidly  with  time. 

As  regards  the  drying  apparatus,  a  proper  drying  cup- 
board with  a  constant  supply  of  heated  air  is  naturally 
the  most  convenient,  but,  failing  this,  the  simplest 
arrangement  is  a  light-tight,  and  as  far  as  possible  air- 
tight, box.  This  should  be  of  generous  size;  24  x  12  x  12 
inches  is  not  too  large  for  a  couple  of  dozen  |  plates. 
The  author  used  for  a  long  time  an  ordinary  metal  deed 
box  with  draught-excluding  rubber  tape  round  the  lid. 
In  the  center  of  the  box  should  be  placed  a  block  of 
wood,  which  should  be  of  a  goodly  size,  for  instance,  for 
the  above  size  box  9x6  inches,  and  of  such  a  height  as 
will  permit  a  flat  dish  to  be  placed  on  top  and  yet  allow 
the  lid  to  be  properly  shut,  with  about  an  inch  to  spare 
above  the  top  of  the  dish.  This  dish  should  be  filled 
with  desiccated  calcium  chloride,  which  can  be  obtained 
from  any  chemical  house.  It  should  not  be  in  too  large 
lumps  nor  in  powder;  about  the  size  of  small  walnuts  or 
chestnuts  is  right. 

The  plates  should  be  arranged  round  the  sides  of  the 
box  with  the  sensitive  surface  facing  the  center;  they 
must  not  be  placed  with  this  side  towards  the  walls  of 
the  box  or  unequal  drying  will  ensue  with  unequal  sen- 
sitiveness and  more  or  less  fog.  It  is  advisable  to  place 
on  the  bottom  of  the  box  two  or  three  layers  of  clean 
stout  blotting  paper,  which  prevents  the  plates  from 
slipping. 


THE  SENSITIVE  PLATES  15 

A  far  more  convenient  arrangement  is  the  use  of  an 
electric  dryer  such  as  is  used  by  hairdressers;  this  can 
be  attached  to  any  electric  light  socket,  and  if  an  endless 
box  be  used  to  confine  the  air  currents,  it  will  be  found 
possible  to  dry  a  dozen  plates  in  less  than  half  an  hour. 
This  is  a  great  advantage,  as  it  may  be  accepted  as  an 
axiom  that  the  more  rapidly  bathed  plates  are  dried,  the 
greater  their  keeping  power  and  the  greater  their  freedom 
from  fog,  with  increased  color-sensitiveness.  The  box 
should  be  about  two  feet  long  and  sufficiently  large  to 
accomodate  two  wooden  drying  racks,  placed  one  behind 
the  other,  but  too  much  space  must  not  be  allowed 
around  the  ends  of  the  racks.  The  dryer  should  be 
placed  at  such  a  distance  from  the  end  of  the  box  that 
the  temperature  half  way  down  the  box  should  be  from 
33°  to  35°  C.  (90°  to  95°  F.). 

Many  dyes  have  been  suggested  for  panchromatizing 
and  more  formulas  for  sensitizing,  but  as  simplicity  and 
ease  of  attaining  results  are  among  the  main  features 
that  have  been  kept  in  view  throughout  this  work, 
but  one  formula  will  be  given,  which  has  proved  to  be 
entirely  satisfactory  in  practice.  The  dye  recommended 
is  that  known  as  sensitol  violet,  and  this  should  be  pre- 
pared in  the  form  of  a  stock  solution,  which  will  keep  in 
the  dark  indefinitely.  The  following  directions,  which 
might  seem  unnecessarily  diffuse  to  the  expert  worker,  are 
thus  given  for  the  benefit  of  those  without  experience.  In 
a  dry  500  ccm  flask  place  i  gram  of  the  dye  and  add  100 
ccm  pure  ethyl  or  methyl  alcohol.  Shake  with  a  cir- 
cular motion  so  as  not  to  distribute  particles  of  the  dye 
on  the  upper  parts  of  the  flask;  then  place  the  flask  in 
a  water  bath  at  about  30°  C.  (84°  F.)  and  raise  the 
temperature  gradually  to  65°  C.  (150°  F.),  giving  the 


16  COLOR  PHOTOGRAPHY 

flask  an  occasional  swirl  round.  Then  add  400  ccm  cold 
alcohol  and  after  shaking  gently  pour  into  the  stock  bot- 
tle; measure  another  200  ccm  of  cold  alcohol  into  the 
flask  and  swirl  round  so  as  to  wash  off  any  adherent 
dye  solution,  then  add  this  to  the  stock  bottle;  now 
pour  300  ccm  distilled  water  into  the  flask  and  after 
shaking  well  add  to  the  stock  bottle.  The  result  will  be 
a  i  :  1000  stock  solution  of  the  dye,  which  must  be  kept 
in  the  dark.  It  may  be  as  well  to  remark  here  that, 
owing  to  the  difficulty  of  making  up  extremely  dilute 
solutions  to  exact  percentages  by  means  of  English 
weights  and  measures,  the  experimenter  in  color  should 
accustom  himself  to  work  in  the  metric  system,  and 
acquire  the  necessary  weights  and  measures.  If  this  be 
impossible,  a  conversion  table  will  be  found  at  the  end 
of  the  book. 

Unfortunately  all  the  isocyanin  dyes,  to  which  class 
this  dye  belongs,  are  more  or  less  sensitive  to  acids  and 
are  more  or  less  decolorized  by  them,  and  when  in  this 
bleached  state  they  have  little  or  no  color-sensitizing 
power.  They  are  so  sensitive  to  acid  that  even  the  small 
amount  of  carbonic  acid  present  in  distilled  water  is 
sufficient  to  decolorize  them,  so  that  it  is  necessary  to 
make  the  water  for  the  actual  bath  alkaline.  Ammonia 
is  the  alkali  generally  used,  but  while  it  is  efficient  it  is 
dangerous,  unless  used  in  very  minute  quantities,  that 
is,  not  more  than  one  or  two  drops  per  100  ccm  of  the 
bath,  as  it  induces  the  rapid  growth  of  fog.  Borax  is  a 
far  better  alkali  to  use,  as  there  is  less  likelihood  of  fog 
with  keeping.  The  actual  sensitizing  bath  is: 

Stock  dye  solution  20  ccm 

Borax,  pure  2  g 

Distilled  water  1000  ccm 


THE  SENSITIVE  PLATES  17 

Dissolve  the  borax  in  the  water  first,  then  add  the  dye 
solution  with  constant  shaking.  The  above  quantity  of 
solution  is  sufficient  to  sensitize  about  500  square  inches 
of  plate  surface,  or  thirty  4x5  plates. 

Slightly  higher  color-sensitiveness  may  be  attained  by 
using  with  the  sensitol  violet  an  admixture  of  orthochrom 
T.  This  dye  should  also  be  made  up  into  a  stock  solu- 
tion in  the  same  way  as  the  violet;  but  the  sensitizing 
bath  will  then  be: 

Stock  sensitol  violet  solution  10  can 

Stock  orthochrom  solution  10  can 

Borax  2  g 

Distilled  water  1000  ccm 

The  advantage  of  this  batn  is  that  a  rather  better  green 
sensitiveness  is  secured,  and  also  slightly  general  higher 
speed  to  white  light,  or,  in  other  words,  the  exposures 
are  slightly  shorter.  The  difference,  however,  is  but 
slight  and  in  practice  the  plain  sensitol  violet  bath  will 
be  found  quite  satisfactory. 

From  the  data  given  above  as  to  the  area  that  may  be 
sensitized  with  these  baths,  it  will  be  seen  that  a  dozen 
plates  will  require  just  400  ccm  of  solution,  so  that  the 
procedure  is  fairly  obvious;  place  four  plates  in  a  dish 
and  flood  them  with  an  even  regular  sweep  with  133  ccm 
of  the  dye  solution.  Rock  the  dish  gently  first  from  side 
to  side  and  then  end  for  end  for  four  minutes,  pour  off 
the  solution  into  a  waste  bottle,  set  the  dish  up  at  an 
angle  so  as  to  allow  the  remains  of  the  solution  to  drain 
down  to  one  corner  and  off.  Then  pour  on  the  plates  300 
ccm  alcohol  (ethyl  or  methyl)  and  rock  the  dish  for  one 
minute.  Remove  the  plates  one  by  one,  giving  them  a 
rinse  urj  and  down  to  make  sure  that  the  dye  solution  ad- 


1 8  COLOR  PHOTOGRAPHY 

herent  to  the  back  of  the  glass  is  rinsed  off  by  the  alcohol. 
Then  place  them  in  the  draining  rack,  not  more  than 
four  plates  to  the  twelve-plate  rack  and  push  the  rack 
into  the  farther  end  of  the  drying  tunnel  which  has  the 
hot  air  blowing  through  it.  The  rack  should  not  be 
pushed  more  than  about  three  inches  into  the  tunnel. 

The  alcohol  used  for  rinsing  may  be  poured  into  a 
graduate,  the  dish  stood  on  end  to  drain  and  four  more 
plates  treated  in  like  manner  with  another  133  ccm  of 
sensitizing  solution.  The  same  alcohol  may  be  used  for 
rinsing  and  again  poured  off  for  the  third  lot  of  plates, 
which  are  treated  in  like  manner.  The  second  batch  of 
plates  should  be  placed  in  another  draining  rack  and 
pushed  into  the  tunnel,  thus  pushing  the  first  rack  nearer 
the  source  of  heat.  The  third  lot  of  plates  is  treated 
in  like  manner  and  placed  in  the  third  rack,  and  by  this 
time,  the  plates  in  the  first  rack  should  be  quite  dry. 

The  racks  should  be  placed  in  the  tunnel  so  that  the 
surface  of  the  plates  is  parallel  with  the  current  of  air, 
and  not  at  right  angles  to  it;  this  ensures  a  complete 
change  of  air  over  the  whole  surface  of  the  plates,  where- 
as if  they  are  placed  at  right  angles  to  the  air-travel, 
only  the  first  plate  gets  the  full  benefit  of  the  hot  air 
and  the  others  are  more  or  less  in  dead  air  pockets. 

This  is  not  the  cheapest  method  of  working,  but  the 
author  has  proved  it  in  practice  to  be  one  of  the  most 
reliable,  and  when  one  considers  that  the  actual  cost  of 
the  dye  and  drying  alcohol  is  approximately  $2.00  for 
thirty  plates  it  is  not  a  serious  item. 

There  are,  of  course,  all  sorts  of  variations  of  this 
procedure.  For  instance  the  whole  400  ccm  of  dye  may 
be  put  into  the  dish  at  once,  and  poured  out  into  a 
graduate  at  the  end  of  the  time  required  to  sensitize 


THE  SENSITIVE  PLATES  19 

each  batch  of  plates,  and  more  alcohol  may  be  used  or 
a  fresh  batch  each  time;  or  the  plates  may  be  lifted  out 
of  the  dye  solution  and  placed  in  another  dish  for  the 
alcohol  bath;  but  the  less  the  plates  are  handled  the  easier 
the  work  becomes.  As  already  stated  either  ethyl  or 
methyl  alcohol  may  be  used;  denatured  spirit  is  danger- 
ous unless  one  knows  what  the  denaturant  is,  and  should 
be  avoided.  There  is  one  point  that  has  not  been  men- 
tioned and  it  is  extremely  important.  If  the  sensitizing 
and  drying  is  carried  on  in  a  room  that  is  used  for 
ordinary  work,  such  as  developing  and  fixing,  it  may  be 
taken  as  an  axiom  that  it  is  impossible  to  prevent  insen- 
sitive and  other  spots  occurring.  The  drying  fan  draws 
the  air  from  the  room  and  any  particle  of  hypo  settling 
on  the  damp  surface  will  cause  an  insensitive  spot, 
while  developer  dust  will  give  rise  to  black  ones.  The 
dimensions  of  the  drying  tunnel  should  be  kept  as  small 
as  possible,  taking  into  consideration  the  size  of  the  dry- 
ing racks.  These  can,  as  a  rule,  be  cut  down  consider- 
ably in  height,  as  the  legs  can  usually  be  shortened. 
The  smaller  the  tunnel  within  reason,  the  more  the  air 
is  confined  and,  therefore,  the  quicker  the  drying. 

Taking  all  things  into  consideration,  there  can  be  no 
question  that  for  the  beginner  in  color  work  commercial 
plates  are  preferable.  Their  keeping  power  is  certainly 
much  greater,  one  is  certain  of  having  them  free  from 
drying  spots  and  stains,  and  most  of  the  makers  issue 
with  each  box  a  card  that  not  only  tells  one  the  correct 
ratio  for  the  filters,  but  also  the  correct  time  of  develop- 
ment to  obtain  a  given  degree  of  contrast.  Above  all 
things,  one  can  obtain  them  backed,  and  thus  there  will 
be  saved  one  of  the  worst  jobs  for  the  home  worker.  A 
backed  plate  gives  much  better  results  than  an  unbacked 


2o  COLOR  PHOTOGRAPHY 

one,  if  the  proper  backing  is  used,  and  as  the  plate  is 
sensitive  to  all  colors  it  is  obvious  that  the  only  efficient 
backing  must  be  black.  It  is  not  a  difficult  matter  to 
make  a  black  backing,  and  one  the  author  has  used 
for  years  is: 

Dextrine  100  g 

Water  100  ccm 

Heat  till  dissolved  and  then  stir  in: 

Ivory  black,  water  color  paste       1000  g 

Continue  stirring  until  thoroughly  incorporated.  As  this 
is  sufficient  for  a  large  number  of  pktes  and  it  is  apt  to 
mould  if  kept,  it  is  advisable  to  stir  in  about  10  ccm  of 
phenol  (carbolic  acid). 

There  is  no  lack  of  commercial  panchromatic  plates, 
as  Eastman  Kodak  Co.  (Wratten  &  Wainwright),  the 
Ilford  Co.  and  the  Cramer  Dry  Plate  Co.  all  issue  plates 
of  excellent  quality  and  color-sensitiveness,  which  may 
also  be  obtained  backed  on  request.  It  would  be  invid- 
ious to  single  out  one  particular  make  as  better  than  the 
others  and  also  unfair;  but  naturally  most  workers  have 
their  own  pet  brand,  as  every  smoker  favors  one  par- 
ticular tobacco.  The  author  in  no  wise  differs  in  this 
respect,  but  his  favoritism  is  based  on  many  years'  use 
of  one  particular  brand  and  while  there  is  very  little 
logical  reason  for  it,  he  always  thinks  that  he  can  obtain 
better  results  with  this  particular  make.  Plates  certainly 
differ  in  their  characteristics;  assuming  that  they  all  have 
the  same  color-sensitiveness,  the  chief  differences  lie  in 
the  velocity  constant  of  development,  and  increase  of  fog 
with  time  of  development.  The  old  advice  that  has  so 


THE  SENSITIVE  PLATES  21 

often  been  given  for  ordinary  work  applies  with  equal 
force  to  color  work;  that  is,  choose  one  plate  and  stick 
to  it. 

As  regards  the  use  of  film  for  color  separation  work, 
the  only  plan  that  can  be  adopted  is  to  use  commercial 
panchromatic  film  and  it  must  be  in  one  piece.  The 
author's  experience  has  proved  that  to  use  three  separate 
films  is  almost  a  hopeless  task,  in  consequence  of  the  un- 
equal expansion  and  contraction  of  the  celluloid  making 
it  practically  impossible  to  obtain  correct  superposition 
of  the  images.  On  the  other  hand,  if  this  must  be  used 
and  the  worker  is  determined  to  sensitize  it  himself, 
the  same  sensitizing  baths  may  be  used,  but  the  alcohol 
bath  must  be  omitted,  or  the  film  will  either  roll  up  into 
a  tight  spill  that  is  utterly  useless,  or  will  be  so  distorted 
by  partial  solution  of  the  celluloid  as  to  be  quite  unwork- 
able. The  sensitizing  bath  can  be  somewhat  improved 
by  the  replacement  of  10  per  cent  of  the  water  by  the 
same  volume  of  methyl  alcohol,  and  after  sensitizing, 
the  film  should  be  washed  for  ten  minutes  in  frequent 
changes  of  distilled  water  to  which  0.2  per  cent  of  borax 
has  been  added. 


CHAPTER  III 
COLOR  FILTERS 

TO  explain  the  action  of  tri-color  filters  it  is  neces- 
sary to  recall  the  statement  that  all  colors  can  be 
formed  from  three  fundamental  colors.  But  while  we 
have  seen  that  these  three  fundamental  colors  give  rise 
to  the  three  color  sensations,  it  must  not  be  thought 
that  there  is  any  closer  connection  between  the  sen- 
sation curves,  shown  in  Fig.  3,  and  color  photography. 
The  color  sensation  curves  are  quite  useless  for  color 
photography,  although  this  is  actually  founded  on  their 
physiological  action,  except  when  we  use  the  additive 
process,  when  the  illumination  of  the  three  positives 
should  be  made  by  the  physiologically  correct  or  funda- 
mental colors.  But  for  subtractive  work,  and  for  the 
making  of  the  negatives  for  the  additive  processes,  the 
color  sensation  curves  are  not  of  the  slightest  practical 
value. 

The  first  essential  is  to  split  up  the  spectrum  or  any 
colored  subject  into  three  regions;  the  one  representing 
all  the  red,  another  all  the  green,  and  the  third  all  the 
blue.  It  has  been  found  that  the  most  satisfactory 
results  are  obtained  when  the  spectrum  is  divided  into 
three  zones,  shown  in  Fig.  6,  in  which  R  represents  the 
region  transmitted  by  the  red  filter,  G  that  of  the  green 
filter  and  B  that  of  the  blue-violet  filter.  A  comparison 
of  the  curves  with  the  color  sensation  curves  in  Fig.  3  will 
at  once  show  that  there  is  but  little  similarity;  in  the 


COLOR  FILTERS  23 

former  the  curves  are  gradual  and  all  three  overlap  one 
another  at  many  points,  whereas  with  the  niters  they 
cannot  be  legitimately  called  curves,  but  are  abruptly 
B  G  R 


400 


460     500 


560  590 


700 


FIG.  6 


ending  regions  with  limited  overlap  at  only  two  points, 
hi  the  golden-yellow,  at  the  D  lines,  from  5900  to  5800, 
and  in  the  blue-green  from  5000  to  4800. 

If  we  separate  these  three  curves  we  shall  obtain  a 
fairly  clear  idea  of  the  action  of  the  filters.    In  Fig.  7,  R 


FIG.  7 

shows  the  action  of  the  red  and  the  blank  portion  is  that 
which  corresponds  to  the  shadows  of  the  negative.  In  G 
the  action  of  the  green  filter  is  shown,  again  with  the 


24  COLOR  PHOTOGRAPHY 

blanks  representing  the  shadows,  and  B  represents  the 
blue  with  the  blank  shadows.  Now  as  it  is  the  shadows 
of  the  negatives  that  print,  the  bare  parts  of  the  above 
diagram  represent  the  parts  that  would  print,  therefore, 
positives  or  prints  from  the  above  would  be  represented 
by  Fig.  8,  in  which  the  black  parts  show  the  parts  that 


FIG.  8 

must  not  show  in  the  additive  process,  that  is  when  we 
project  by  colored  lights;  while  in  sub  tractive  processes, 
that  is  in  prints,  they  represent  the  colors  that  must  be 
present.  We  may,  therefore,  tabulate  these  results  as 
follows: 


Filter 

Additive  process 
Projecting  color 

Subtractive  pro- 
cess Printing 
color 

Red 
Green 

Red 
Green 

Blue-green 
Red 

Minus  blue 
Minus  red 

Blue-violet 

Blue-violet 

Yellow 

Minus  yellow 

COLOR  FILTERS  25 

It  will  thus  be  seen  that  one  may  assume  that  the  sub- 
tractive  printing  colors  are  the  complementaries  of  the 
filter  colors,  and  for  this  reason  the  corresponding  nega- 
tives are  frequently  referred  to  as  the  "minus  color" 
plates,  as  shown  in  the  fourth  column. 

As  the  limits  of  the  transmission  of  the  niters  are  set 
by  the  above  statement,  we  have  merely  to  make  filters 
that  will  show  these  cuts.  The  most  satisfactory  method 
is  by  the  use  of  aniline  dyes,  dissolved  in  gelatine  and 
cemented  between  glasses  to  protect  the  stained  film 
from  damp  and  mechanical  injury,  for  every  photog- 
rapher knows  that  gelatine  readily  absorbs  moisture, 
and  that  it  is  easily  damaged  by  dirty  or  damp  fingers. 

In  the  early  days  of  color  photography  it  was  usual  to 
employ  glass-sided  cells  filled  with  colored  solutions,  and 
they  are  still  employed  sometimes  in  commercial  estab- 
lishments, such  as  photo-mechanical  studios.  But  for 
the  dilettante  they  are  the  most  unsatisfactory  form  of 
filter  that  can  be  used,  and  also  when  of  sufficiently  good 
quality  to  allow  large  aperture  lenses  to  be  used,  are 
very  costly,  so  that  we  shall  not  take  them  into  con- 
sideration at  all.  The  preparation  of  the  correct  filters 
does  not  present  insurmountable  difficulties  for  the  aver- 
age worker,  and  it  should  be  looked  upon  as  part  of  the 
preliminary  training  for  every  worker  to  make  a  set  of 
filters.  Yet  it  must  not  be  overlooked  that  it  is  actually 
much  more  expensive  to  make  them  and  the  results  are 
rarely  as  satisfactory  as  the  commercial  filters.  How- 
ever, we  will  proceed  to  describe  the  preparation  of  a  set. 

The  apparatus  required  will  be  a  sheet  of  plate  glass, 
not  less  than  lox  12  inches  in  size  and  about  half  an 
inch  thick;  three  leveling  screws  and  a  level;  some 
sheets  of  plate  glass  about  one-fourth  inch  thick  and 


26  COLOR  PHOTOGRAPHY 

sufficiently  large  to  allow  a  margin  of  at  least  one-fourth 
inch  all  round  the  largest  filter  that  is  required;  a  beaker 
of  500  ccm  capacity,  another  of  100  ccm,  and  an  accu- 
rate 10  ccm  pipette.  The  materials  required  are  some 
soft  photographic  gelatine,  of  which  about  100  g  will 
be  ample,  and  small  quantities  of  the  following  dyes; 
rose  Bengal,  tartrazin,  patent  blue,  acid  rhodamin,  tolui- 
din  blue  and  naphthol  green.  About  10  g  of  each  will 
be  plenty.  We  also  need  some  squares  of  patent  white 
plate  glass,  about  one-sixteenth  inch  thick  and  of  the 
necessary  size  to  cover  the  lens  completely  without  cut- 
ting off  any  of  the  light  from  the  plate,  and  some 
Canada  balsam,  dissolved  in  xylol,  as  used  by  micro- 
scopists,  which  can  be  obtained  commercially;  it  should 
be  noted  that  a  chloroform  solution  of  the  balsam  must 
not  be  used. 

The  large  sheet  of  glass  is  merely  used  as  a  support 
for  the  gelatine-coated  glass,  so  that  the  film  shall  set 
of  an  even  thickness  all  over,  and  therefore,  its  ac- 
tual size  is  not  of  real  moment.  It  is  frequently  pos- 
sible to  pick  up  a  fairly  large  piece  from  a  glass  dealer 
at  a  very  reasonable  price,  because  scratches  and  flaws 
will  not  matter.  The  smaller  pieces  of  glass,  one-quar- 
ter inch  thick,  are  used  to  coat  the  dyed  gelatine  on, 
while  the  one-sixteenth  inch  pieces  are  used  for  the  final 
filter.  Both  should  have  perfect  surfaces.  The  reader 
may  possibly  wonder  why  the  dyed  gelatine  cannot  be 
coated  directly  on  its  final  support;  if  this  were  done, 
the  chances  are  that  the  filter  would  not  be  flat,  for  the 
gelatine  contracts  in  drying  and  distorts  the  glass,  that 
is  bends  it  into  a  shallow  curve,  and  the  result  would  be 
that  the  filter  would  slightly  alter  the  focus  of  the  lens; 
as  this  filter  curvature  might  not  be  equal  in  all  three 


COLOR  FILTERS  27 

filters,  the  foci  for  the  three  colored  images  would  differ 
and  the  images  would  be  of  unequal  size,  and  possibly 
not  equally  sharp,  and  as  we  have  to  accurately  super- 
impose the  constituent  positives,  the  outlines  of  the  sub- 
ject would  not  coincide  and  a  confused  jumble  would  be 
the  result,  or  we  would  get  color  fringes. 

For  this  reason  also,  it  is  important  that  the  final  filter 
glass  be  flat,  and  this  is  one  of  the  difficulties  in  making 
filters,  that  is,  to  obtain  six  pieces  of  glass  that  are  suffi- 
ciently flat  to  be  serviceable.  To  test  the  glass  for  flat- 
ness, place  it  on  a  flat  black  support  such  as  a  focusing 
cloth  or  piece  of  velvet,  this  being  placed  at  an  angle  of 
45  degrees  on  a  table  about  six  feet  from  a  window; 
then,  on  looking  down  on  it,  the  image  of  the  cross  bars 
of  the  window  will  be  seen  reflected  and  usually  a  double 
image,  one  from  the  front  and  a  fainter  one  from  the 
back  of  the  glass.  If  the  glass  or  the  eye  be  now  moved 
so  that  the  images  are  reflected  from  all  over  the  surface, 
we  can  easily  see  whether  the  two  surfaces  are  parallel, 
as  then  the  two  images  will  keep  the  same  distance 
apart,  whereas  if  lenticular  they  will  either  diverge  or 
converge.  Pieces  showing  this  defect  should  be  rejected. 
If  the  images  are  not  straight,  the  glass  is  also  curved. 
It  has  been  assumed  that  the  glass  is  bought  cut  to  the 
required  size;  if  it  is  bought  in  a  large  sheet  it  can  be 
examined  in  the  same  way  and  the  flat  parts  marked 
with  a  piece  of  soap  and  subsequently  cut  out;  but 
this  presumes  knowledge  of  how  to  cut  glass  with  a  dia- 
mond or  wheel.  This,  like  everything  else,  is  extremely 
easy  when  you  know  the  trick,  but  it  will  probably  be 
better  to  purchase  the  glass  ready  cut  and  select  the 
good  pieces. 

The  size  of  the  filter  is  easily  determined,  and  a  rough 


2g  COLOR  PHOTOGRAPHY 

and  ready  way  is  to  measure  the  diameter  of  the  lens 
hood,  not  the  glass,  and  aUow  one-quarter  inch  beyond 
this;  this  is  assuming  that  the  filter  is  to  be  used  on  the 
lensi  as  it  will  be  seen  later  that  there  are  other  positions. 
A  more  correct  method  is  to  use  a  diagram  such  as  is 
shown  in  Fig.  9,  in  which  L  represents  the  lens  racked 
out  from  the  plate  PP,  to  its  equivalent  focus;  then,  by 
drawing  a  line  from  the  corner  of  the  diagonal  of  the 


Fig.  9 

plate  through  the  lens,  the  size  of  the  filter  can  be  at 
once  determined  by  actual  measurement,  as  the  distance 
between  the  line  from  the  corner  of  the  plate  to  the 
straight  line  A  which  is  a  prolongation  of  the  optical 
axis  of  the  lens  will  give  at  once  half  of  the  necessary 
width  of  the  filter.  Obviously  the  further  the  filter  is 
from  the  lens  the  larger  it  must  be  if  it  is  not  to  curtail 
the  field  or  the  light. 

The  gelatine  solution  is  prepared  as  follows:   Distilled 
water  must  be  used  and  it  is  well  to  make  up  a  generous 


COLOR  FILTERS  29 

quantity  of  the  solution,  say  about  400  ccm,  as  it  is 
decidedly  better  to  waste  some  than  to  run  short.  As 
a  10  per  cent  solution  is  required,  we  weigh  out  40  g  of 
gelatine,  place  in  the  500  ccm  beaker,  cover  with  distilled 
water  and  stir  it  well  for  two  or  three  minutes,  then  pour 
the  water  off  and  repeat  the  washing,  allowing  the 
gelatine  to  soak  for  ten  minutes  the  second  time  and 
fifteen  minutes  the  third,  stirring  it  occasionally.  Then 
as  much  water  as  possible  should  be  pressed  out  by 
means  of  a  glass  rod  and  the  beaker  placed  in  hot  water 
at  55°  C.  (130°  F.),  when  the  gelatine  will  gradually 
melt  in  the  water  that  it  has  absorbed  and  enough  more 
is  added  to  make  the  bulk  up  to  400  ccm.  The  solution 
should  now  be  filtered  through  a  double  thickness  of 
well  washed  and  wetted  linen;  an  old  handkerchief  does 
well  for  this. 

The  dye  solutions  are  preferably  prepared  in  the  form 
of  stock  solutions  as  follows:  i  g  to  100  ccm  for  rose 
Bengal,  patent  blue,  acid  rhodamin  and  naphthol  green; 
2  g  to  100  ccm  for  tartrazin  and  0.5  g  to  100  ccm  for 
toluidin  blue.  These  quantities  should  be  placed  in 
clean,  well-dried  bottles,  100  ccm  of  hot  distilled  water 
added,  the  bottles  well  shaken  for  half  an  hour  and 
then  allowed  to  stand  so  that  the  solutions  may  settle. 
The  quantities  of  the  dye  (not  solutions)  needed  for  the 
average  size  of  filter  are  very  small  and,  therefore,  the 
amounts  for  a  square  meter  are  given,  from  which  it 
will  be  easy  to  calculate  that  for  any  given  size: 

For  the  red  filter: 

Rose  Bengal  1.25  g 

Tartrazin  2.0   g 


30  COLOR  PHOTOGRAPHY 

For  the  green  filter: 

Naphthol  green  0.4  g 

Patent  blue  0.2  g 

Tartrazin  i.o  g 

For  the  blue  filter: 

Acid  rhodamin  0.6    g 

Toluidin  blue  1.8    g 

The  usual  quantity  of  gelatine  solution  employed  is  700 
ccm  per  square  meter,  which  gives  a  dry  filter  thickness 
of  about  0.4  mm;  it  is  advisable  to  adhere  always  to  a 
given  volume  of  dyed  gelatine  for  a  given  area. 

We  can  now  prepare  the  glass.  This  should  be  placed 
in  a  mixture  prepared  as  follows.  Make  the  following 
solution: 

Potassium  bichromate  50  g 

Water  250  ccm 

Then  add  gradually: 

Sulphuric  acid  25  ccm 

Stir  well  and  add: 

Water  to  make  1000  ccm 

Fill  a  developing  tray  with  this  solution  and  immerse 
the  glasses,  using  a  flat  strip  of  wood  to  lift  them,  as 
the  solution  bites  the  skin.  Really  the  best  way  to  clean 
the  glasses  is  to  immerse  one  at  a  time  and  scrub  the 
surface  with  an  old  tooth  brush  or  a  temporary  mop, 
made  by  tying  some  old  rags  round  the  end  of  a  short 
stick,  then  turn  the  glass  over  and  scrub  the  other  side, 
lift  out  with  a  stick  and  drop  it  into  hot  water,  then 
start  cleaning  another  glass  and  remove  the  first  from 
the  hot  water,  give  it  a  rinse  in  distilled  water  and  put 


COLOR  FILTERS  31 

in  a  rack  to  dry.  Then  put  the  second  glass  in  the  hot 
water  and  finish  all  in  this  way.  It  is  possible  to  put 
six  or  more  glasses  hi  to  the  cleaning  liquid  at  one  time, 
but  in  doing  so  there  is  a  very  great  chance  of  scratching 
one  or  more  of  the  glasses  with  a  sharp  edge  or  corner, 
and  although  cleaning  them  singly  is  more  trouble  and 
takes  more  time,  it  pays  in  the  end. 

When  the  glasses  are  dry  they  should  be  carefully 
polished  with  a  clean  rag.  These  glasses  are  used  for 
the  first  coating  and  the  dried  dyed  film  has  to  be 
stripped  from  them,  but  unless  they  are  perfectly  clean 
it  will  not  peel,  and  even  then  it  is  not  always  an  easy 
matter.  All  sorts  of  dodges  have  been  suggested,  such  as 
collodionizing  the  glass,  waxing  it,  or  polishing  with  talc; 
but  we  may  be  content  with  a  very  simple  plan.  Add 
about  ten  drops  of  almond  or  olive  oil  to  100  ccm  of 
benzol,  pour  five  or  six  drops  of  this  on  the  glass  and  rub 
over  with  a  tuft  of  absorbent  cotton,  and  then  polish 
with  two  pieces  of  clean  dry  linen.  An  old  handkerchief 
again  comes  in  handy,  as  it  is  usually  fluffless;  this  will 
clean  the  surface  and  yet  leave  the  merest  trace  of  oil, 
which  makes  it  easy  to  strip  afterwards. 

If  the  size  of  the  finished  filters  were  to  be  5  x  5  cm, 
we  would  naturally  choose  the  first  glasses  12  x  12  cm, 
so  as  to  get  four  filters  from  each  sheet,  which  gives  a 
chance  to  pick  and  choose.  To  cover  144  qcm  at  the 
rate  of  700  ccm  per  square  meter,  we  shall  require  10 
ccm  of  dyed  gelatine  and  very  small  quantities  of  the 
dyes,  for  instance  in  the  case  of  rose  Bengal  0.018  g  and 
0.028  g  tartrazin,  which  means  1.8  ccm  of  the  first  solu- 
tion and  1.4  ccm  of  the  second.  While  it  is  possible  to 
measure  these  quantities  with  a  good  pipette,  it  is  pref- 
erable to  make  at  least  50  ccm  of  the  dyed  gelatine; 


32  COLOR  PHOTOGRAPHY 

we,  therefore,  measure  34  ccm  of  the  plain  gelatine 
solution,  mix  9  ccm  of  the  rose  Bengal  solution  and  7 
ccm  of  the  tartrazin,  and  add  these  to  the  gelatine  solu- 
tion; after  stirring  well,  10  ccm  should  be  coated  on  the 


Every  worker  has  his  own  particular  method  of  work- 
ing, and  the  author  is  addicted  to  the  use  of  the  pipette 
for  coating,  as  it  has  been  found  easier  to  lead  the  gela- 
tine over  the  surface  of  the  glass  with  this  than  by  pour- 
ing out  of  a  small  graduate,  and  there  is  less  chance  of 
bubbles.  If  these  do  occur  they  can  very  easily  be  led  to 
the  edge  of  the  glass,  where  they  will  do  no  harm,  and 
can  be  broken  by  touching  with  a  spill  of  blotting  or 
filter  paper. 

It  is  important  that  the  room  in  which  the  coating  is 
done  be  not  too  cold  or  the  gelatine  will  set  before  it  is 
possible  to  spread  it  over  the  glass,  and  the  stock  of 
dyed  gelatine  should  be  kept  at  a  proper  temperature. 
It  is  easy  to  do  this  with  a  water  bath,  and  45°  C. 
(123°  F.)  is  a  comfortable  temperature  to  work  at,  as 
the  gelatine  can  then  be  easily  spread,  and  it  sets  rather 
rapidly  to  an  even  surface.  As  soon  as  thoroughly  set, 
the  coated  glass  should  be  reared  up  on  edge  to  dry 
and  the  method  suggested  for  drying  sensitized  plates 
may  be  adopted,  but  dust  must  be  carefully  guarded 
against,  and  before  commencing  to  coat,  the  working 
bench  should  be  well  washed  down  with  water  so  as  to 
ensure  that  no  dust  lies  about.  Rapid  drying  is  not  of 
such  moment  with  niters  as  with  sensitized  plates,  but  it 
should  be  as  even  as  possible;  if  it  takes  too  long,  the 
film  may  become  pitted  with  small  colonies  of  spots  due 
to  bacterial  growth,  particularly  in  hot  weather. 

When  the  gelatine  is  perfectly  dry,  it  should  be  cut  all 


COLOR  FILTERS  33 

round  the  edges,  about  2  mm  inside,  with  a  sharp  pen- 
knife, and  usually  it  is  possible  to  lift  one  edge  with  the 
knife  and,  by  taking  hold  of  the  free  edge,  to  strip  the 
whole  film;  if  not,  it  should  be  held  for  four  or  five  min- 
utes about  two  feet  above  a  bowl  of  steaming  water, 
when  it  should  strip  without  trouble  and  without  stretch- 
ing. As  soon  as  stripped,  the  film  should  be  placed  be- 
tween tissue  paper  and  stored  between  the  leaves  of  a 
book.  The  used  glasses  can  be  freed  from  the  narrow 
strip  of  dyed  gelatine  by  scraping  with  the  knife,  re- 
polished,  and  again  coated  with  the  second  lot  of  dyed 
gelatine,  but  it  is  preferable  to  have  at  least  six  glasses 
and  coat  them  one  after  the  other,  thus  making  one  job 
of  it.  Naturally  the  pipette  will  be  well  scoured  out 
with  hot  water. 

It  will  be  seen  that  the  process  is  not  such  a  difficult 
one  and  with  a  little  practice  it  is  easy  to  become  so 
expert  that  a  failure  is  rarely  met  with.  But  for  years 
the  author  has  given  up  coating  his  own  filters,  except 
for  experimental  purposes,  and  is  content  to  buy  com- 
mercial filters.  The  results  are  absolutely  certain  and  the 
actual  cost  is  so  very  little,  that  taking  into  considera- 
tion the  difficulty  of  getting  good  glass  and  the  fact 
that  one  has  to  buy  much  larger  quantities  of  dyes  than 
one  needs,  commercial  filters  actually  work  out  cheaper 
in  the  end. 

Commercial  filters  can  be  obtained  in  the  form  of  film 
or  cemented  between  glasses.  Assuming  that  the  worker 
has  made  his  own  filters  or  bought  commercial  film 
filters,  we  come  to  the  operation  of  cementing  them, 
which  is  not  nice.  The  final  glass  must  be  carefully 
cleaned  and  the  polished  surfaces  should  be  placed  in 
contact,  pair  by  pair.  We  now  want  to  fasten  these 


34  COLOR  PHOTOGRAPHY 

together  like  a  book  cover,  and  use  for  this  purpose  a 
piece  of  lantern-slide  binding,  making  quite  sure  that 
the  edges  are  even.  This  can  easily  be  done  by  placing 
the  wetted  strip  on  a  yielding  surface,  such  as  an  open 
book;  then,  holding  the  two  glasses  together,  lower  them 
on  to  the  strip  with  an  equal  margin  on  each  side, 
press  down,  and  rub  the  edges  of  the  strip  into  contact 
with  the  sides  of  the  glass.  There  is  no  need  to  let  this 
get  absolutely  dry,  but  it  should  not  be  wet.  The  dyed 
film,  cut  to  the  same  size  as  the  glass,  is  slipped  be- 
tween the  two  glasses  and  all  edges  made  to  coincide. 
The  filter  should  now  be  laid  down  on  a  sheet  of  hard 
card  or  paper,  the  top  glass  and  the  gelatine  film 
lifted  up  together,  and  a  pool  of  balsam  poured  on  the 
lower  glass  near  the  hinge.  Enough  balsam  should  be 
used  to  cover  about  one-fourth  of  the  surface  of  the 
glass.  The  gelatine  film  should  then  be  carefully  lowered 
down  on  the  balsam,  another  pool  of  balsam  poured  on 
the  gelatine  and  then  the  top  glass  lowered.  Gentle 
pressure,  starting  from  the  hinge,  will  force  the  balsam 
out  to  all  the  edges  without  the  least  air  bubble.  If  one 
does  show,  it  can  be  chased  to  the  edge  by  pressure  of 
the  fingers.  A  good  sized  metal  bulldog  clip  should  now 
be  clipped  on  the  glass  at  right  angles  to  the  hinge,  as 
far  in  as  it  will  go  and  then  another  applied  opposite  the 
first;  the  paper  hinge  should  be  scraped  off  the  edge 
with  a  knife,  paying  no  attention  to  that  on  the  flat  of 
the  glass,  and  a  clip  placed  here  and  then  one  on  the 
fourth  side.  The  filter  may  then  be  reared  up  on  one 
corner  to  allow  the  balsam  squeezed  out  from  its  edges 
to  run  down.  When  all  the  filters  are  cemented,  begin 
with  the  first,  wipe  off  the  exuded  balsam  with  filter 
paper  or  a  bit  of  old  rag,  and  leave  the  filters  to  dry. 


COLOR  FILTERS  35 

They  really  require  a  warm  place  and  should  be  left 
three  weeks  in  a  flat  position,  so  that  as  soon  as  the  first 
lot  of  exuded  balsam  has  been  wiped  off  they  should  be 
placed  flat  on  a  glass  or  shelf  with  a  piece  of  paper 
underneath  them,  as  the  balsam  that  exudes  will  cement 
them  to  any  thing  that  they  touch.  Balsam  is  one  of 
the  stickiest  of  all  sticky  substances  and  the  best  way 
to  clean  the  fingers  is  to  well  wet  newspaper  with  de- 
natured alcohol  and  rub  well,  using  as  much  clean  paper 
as  possible  and  then  benzol  and  paper,  followed  by 
plenty  of  soap  and  hot  water. 

An  alternative  method  is  to  leave  the  hinge  on,  place 
the  filter  on  a  thickness  or  two  of  blotting  paper  on  a 
level  surface  and  place  a  card  on  top  with  a  good-sized 
weight,  four  pounds  not  being  too  heavy  for  a  12x12 
cm  filter.  Direct  heat  cannot  be  used  for  drying,  as  this 
causes  the  edges  to  dry  first  and  gives  rise  to  distortion. 

At  the  end  of  the  three  weeks  the  exuded  balsam 
should  be  scraped  off,  and  the  glass  cleaned  with  alcohol 
and  newspaper,  then  with  bits  of  cloth  and  finally 
polished.  Do  not  try  to  be  sparing  with  the  cleaning 
cloth,  or  use  one  large  cloth;  little  bits  and  each  piece 
thrown  away  as  soon  as  it  gets  sticky  is  the  easiest  way. 
The  final  polishing  should  be  done  with  tissue  paper  and 
alcohol,  following  the  same  plan,  that  is,  fresh  pieces 
continually.  Benzol,  xylol  or  chloroform  should  not  be 
used,  as  they  are  energetic  solvents  of  balsam  and  will 
almost  inevitably  creep  in  between  the  edges,  in  which 
case  the  job  will  have  to  be  done  all  over  again. 

Those  who  would  like  to  make  their  own  preparation 
of  balsam  may  purchase  some  dried  Canada  balsam  from 
a  lens  worker  or  optician.  This  should  be  roughly 
powdered,  which  is  most  easily  done,  though  it  is  rather 


36  COLOR  PHOTOGRAPHY 

wasteful,  by  tying  it  up  in  a  cloth  and  hammering  it 
with  a  heavy  hammer;  a  fine  powder  is  not  wanted  but 
the  big  pieces  should  merely  be  broken  up.  Then  place 
this  in  a  wide  mouthed  bottle,  place  in  the  water  bath 
and  bring  the  latter  slowly  to  a  boil,  stirring  the  balsam 
all  the  time;  add  about  one  fifth  of  its  weight  of  xylol, 
stirring  well  and  then  letting  it  get  cold  in  the  water 
bath.  This  preparation  requires  a  much  higher  tempera- 
ture to  melt  and  must  be  used  hot.  It  then  sets  very 
quickly  and  at  a  pinch  a  filter  thus  cemented  may  be 
used  the  next  day.  The  only  difficulty  likely  to  be  met 
with  is  the  setting  of  the  balsam  before  an  even  film  is 
obtained,  but  warming  the  glasses,  or  keeping  them  on 
a  hot  plate  for  some  time  under  pressure  will  soon  make 
the  balsam  spread  out. 

There  are  four  possible  positions  for  the  filter;  in 
front  of  the  lens;  between  the  combinations  close  to  the 
diaphragm;  behind  the  lens;  and  immediately  in  con- 
tact with  the  sensitive  surface.  Between  the  lenses  is 
the  very  worst  place  to  choose,  although  this  requires 
the  smallest  filter,  as  is  obvious.  In  the  first  place,  it 
is  very  likely  to  upset  the  corrections  of  the  lens,  particu- 
larly with  the  later  forms  of  anastigmatic  lenses,  and 
with  these  there  is  often  not  enough  room  to  insert  any 
other  than  a  film  filter.  Secondly,  it  is  not  easy  to 
change  the  filters  in  this  position  without  some  special 
fitting,  so  that  we  can  dismiss  this  at  once.  Either  in 
front  of  or  behind  the  lens  may  be  chosen,  which  one 
being  a  matter  of  indifference,  provided  focusing  is 
always  effected  through  the  filter,  a  matter  that  we 
shall  have  to  deal  with  later  on  when  talking  of  screen 
plates  (See  Chapter  XII).  In  either  case  some  sort  of 
sliding  fitting  is  advisable,  although  this  is  not  conven- 


COLOR  FILTERS  37 

lent  in  some  cases  inside  the  camera,  as  not  only  may 
the  rear  lens  protrude  beyond  the  lens  board,  but  one 
has  to  have  some  means  of  shifting  the  filter  between 
exposures,  which  necessitates  a  light-tight  fitting. 

It  is  possible  in  many  cases  to  arrange  a  frame  to 
slide  over  the  camera  front,  and  to  fit  the  ordinary  lens 
panel  on  this,  so  that  the  filters  will  be  behind  the  lens. 
The  sliding  frame  can  be  made  on  the  same  lines  as  the 
usual  lantern  slide  carrier,  and  if  velvet  is  used  to  line 
the  outer  frames  there  will  be  no  trouble  in  making  it 
light-tight.  Or  it  may  be  possible  to  fit  such  a  frame  on 
the  lens  barrel  itself,  but  here  it  must  be  so  securely 
fastened  that  there  is  no  chance  of  its  slipping  off. 
Really  the  simplest  plan  is  to  obtain  one  of  the  square 
slip-on  cells,  which,  fitting  on  the  lens  hood  or  barrel, 
may  be  always  retained  in  position  and  the  filters  merely 
lifted  out  and  inserted  as  required.  It  is  advisable,  if 
possible,  to  remove  the  lens  hood  and  fit  the  holder  on 
the  barrel,  as  this  means  not  only  slight  reduction  in 
size,  but  as  a  rule  a  firmer  hold.  In  order  to  obtain  the 
correct  size  of  fitting,  the  diameter  of  the  lens  tube 
should  be  taken  with  a  pair  of  sliding  calipers.  Failing 
these,  the  next  best  plan  is  to  take  a  narrow  strip  of  hard 
writing  paper  and  wrap  round  the  lens  barrel  so  that  the 
ends  overlap  by  about  half  an  inch,  then  with  a  sharp 
penknife  cut  right  through  both  pieces  of  paper  midway 
of  the  overlap,  not  at  the  end. 

Placing  the  filter  close  to  the  plate  means  that  the 
filter  must  be  of  the  same  size  as  the  plate.  Defects  in 
the  filter,  such  as  want  of  absolute  parallelism  of  the 
surfaces,  are  here  of  the  least  consequence;  but  local 
defects,  such  as  coating  striae  or  bubbles,  are  more 
apparent  on  the  negative  image,  though  only  locally. 

49382 


3  8  COLOR  PHOTOGRAPHY 

Special  sliding  backs  can  be?  obtained  commercially,  fit- 
ted with  the  three  niters  and  made  to  take  three  plate- 
holders,  or  with  some  plate-holders,  particularly  of  the 
English  book-form  pattern,  the  filter  may  be  placed  in 
actual  contact  with  the  sensitive  surface;  then  naturally 
its  thickness  must  be  allowed  for  in  focusing. 

One  important  point  in  the  choice  of  filter  fittings, 
particularly  metal  ones,  is  that  there  should  be  no 
abnormal  pressure  on  the  glasses,  as  this  may  cause 
strain  and  consequent  degradation  of  definition.  It 
should  be  possible  to  turn  the  filter  round,  or  shift  it, 
with  the  lightest  pressure  of  the  fingers.  Neither  is  it 
advisable  to  use  cells  screwing  into  the  lens  hood,  as 
this  is  almost  certain  to  shake  the  camera  and  there 
is  much  loss  of  time  in  changing. 

For  photomechanical  work,  in  which  long-focus  lenses 
are  nearly  always  used  with  half-tone  screens,  the  glass 
must  be  optically  worked,  as  carefully,  in  fact,  as  the 
lenses  themselves.  Such  glasses  are  known  commercially 
as  " optical  flats,"  and  are  very  costly  if  of  any  size. 
They  must  all  be  absolutely  the  same  thickness  and  be 
so  arranged  that  they  are  always  perpendicular  to  the 
axis  of  the  lens. 

The  ordinary  filters  may  be  used  for  making  the  sepa- 
ration negatives  for  photomechanical  work,  as  if  there  is 
not  absolute  coincidence  of  size,  this  can  be  corrected  by 
the  operator  when  making  the  screen  negatives  from  the 
transparencies,  though  he  will  not  be  pleased  at  having 
to  do  this. 

It  may  possibly  be  as  well  to  interpolate  here  a  note 
as  to  the  making  of  the  constituent  negatives  for  photo- 
mechanical purposes.  The  use  of  the  panchromatic 
gelatine  plate  for  this  work  is  largely  on  the  increase, 


COLOR  FILTERS  39 

and  in  some  cases  the  slow  panchromatic  plate  is  used 
for  making  the  color  separation  and  the  screen  negatives 
in  one;  but  the  usual  practice  is  to  make  the  separation 
negatives  first,  from  these  a  set  of  transparencies,  and 
then  the  screen  negatives.  It  may  be  noted  that  the 
transparencies  for  such  work  should  be  as  little  like  a 
lantern  slide  as  possible.  They  should  be  fully  exposed, 
quite  "soft"  in  character,  and  with  practically  no  bare 
glass  except  in  the  very  deepest  shadows.  Full  exposure 
should  be  given  to  the  plates,  and  it  is  better  to  use  slow 
negative  rather  than  transparency  plates  for  this  work, 
as  giving  a  longer  range  of  gradation  and  less  tendency 
to  brilliancy.  The  exposure  should  be  full  and  develop- 
ment not  pushed  too  far,  so  that  the  highest  densities 
are  quite  transparent. 

In  many  commercial  process  establishments  collodion 
emulsion,  and  even  the  wet  plate  process,  still  hold  their 
own  for  the  making  of  the  separation  negatives,  and  also 
the  combined  separation-screen  negatives.  Usually  the 
emulsion  is  obtained  commercially  with  its  special  sen- 
sitizers,  and  the  makers  issue  instructions  for  the  making 
of  the  filters,  which  are  usually  of  the  liquid  cell  type, 
for  use  with  the  same.  On  the  other  hand  the  method  of 
sensitizing  already  advised  may  be  adopted,  or  the  dye 
may  be  added  to  the  enrulsion,  and  in  this  case  80  ccm 
of  sensitol  violet  stock  solution  should  be  added  to  1000 
ccm  of  the  plain  emulsion,  and  the  plates  washed  in  run- 
ning water  or  under  a  rose  tap  for  fifteen  minutes.  The 
washing  increases  the  sensitiveness  of  the  plates  about 
five  times. 

By  some  writers  it  has  been  proposed  to  use  different 
plates  for  the  different  color  separations,  that  is  to  say, 
an  ordinary,  non-color-sensitive  plate  for  the  minus 


40  COLOR  PHOTOGRAPHY 

yellow  negative;  an  orthochromatic  plate  for  the  minus 
red  negative;  a  panchromatic  or  red-sensitive  one  for 
the  minus  blue  negative.  This  plan  may  at  first  sight 
appear  to  have  certain  advantages,  but  this  method  is 
not  one  that  should  be  adopted.  It  is  a  well  established 
fact  that  the  degree  of  contrast,  or  gamma,  differs 
with  different  kinds  of  plates,  and  in  fact  with  different 
batches  of  the  same  kind  of  plate,  to  say  nothing  of  the 
development  velocity  of  the  plates,  and  one  of  the  most 
important  essentials  in  making  separation  negatives  is  to 
have  them  of  the  same  degree  of  contrast  as  far  as  pos- 
sible. That  is  to  say,  in  the  three  negatives  the  range 
of  densities  of  a  black  and  white  scale  should  be  the 
same;  and  with  three  totally  different  kinds  of  plates 
this  is  almost  an  impossibility.  One  kind  of  plate 
should  be  used  for  all  three  separation  negatives,  and 
they  should  be,  as  already  pointed  out,  as  far  as  con- 
venient, developed  together.  The  adoption  of  this  plan 
will  save  no  end  of  after  manipulation  and  dodging  in 
getting  concordant  results;  and  it  may  be  taken  as  an 
axiom  that  hand  work,  except  for  the  removal  of  purely 
mechanical  defects,  such  as  pinholes,  etc.,  cannot  be  suc- 
cessfully executed  with  color  negatives. 


CHAPTER  IV 
THE  DARKROOM 

AS  the  plates  used  for  color  photography  are  sen- 
sitive to  all  colors,  it  is  obvious  that  we  cannot  use 
the  normal  red  light  for  illumination  of  the  dark  room, 
and  if  this  were  reduced,  as  it  can  be,  so  as  to  be  safe 
for  the  panchromatic  plate,  the  light  would  be  so  weak 
that  it  would  be  practically  impossible  to  see  anything. 
It  is  an  established  fact,  however,  that  the  eye  is  seven 
hundred  times  more  sensitive  to  green  light  than  to  red, 
therefore,  a  deep  green  light  is  used  for  color  work.  But 
even  with  this  it  must  not  be  forgotten  that  the  plate  is 
sensitive  to  green,  hence  undue  exposure  of  the  plate 
should  be  avoided,  and  it  is  advisable  either  to  work  in 
the  shadow  of  the  lamp,  or  to  provide  a  cover  for  the 
dish;  the  former  is  preferable,  as  it  enables  one  to 
rock  the  dish  during  development. 

Green  safelights  can  be  obtained  commercially  and 
also  green-stained  papers,  which  can  be  placed  between 
two  glasses  and  used  instead  of  the  ordinary  red  screen. 
They  can  be  also  home-made,  and  as  they  do  not  require 
such  a  careful  adjustment  of  the  quantity  of  the  dyes  as 
taking  niters,  they  are  fairly  easy  to  make.  They  require 
no  other  dyes  than  those  used  for  the  filters,  that  is,  one 
can  use  naphthol  green,  patent  blue  and  tartrazin,  or 
instead  of  the  patent  blue,  brilliant  acid  green  may  be 
used.  A  suitable  formula  is: 

Patent  blue  1.75  g 

Naphthol  green  1.75  g 

Gelatine,  8  per  cent  solution         700  ccm 
41 


42  COLOR  PHOTOGRAPHY 

This  is  sufficient  for  i  square  meter.    This  screen  should 
be  bound  up  with  another  one  prepared  from: 
Tartrazin  5-5  g 

Gelatine,  8  per  cent  solution         700  ccm 

When  dry  the  two  niters  should  be  bound  up  together 
with  a  piece  of  tissue  paper  in  between  to  diffuse  the 
light.  Only  the  two  sides  of  this  safelight  should  be 
bound;  the  top  and  bottom  should  be  left  free,  so  that 
any  moisture,  which  might  be  driven  out  by  the  heat  of 
the  lamp,  may  escape.  It  is  preferable  to  place  the  yel- 
low-coated glass  next  the  light  source.  The  patent  blue 
in  the  above  formula  may  be  replaced  by  brilliant  acid 
green  with  equally  satisfactory  results. 

It  is  possible,  however,  to  make  these  safelights  by 
merely  soaking  old  plates  in  dye,  or  even  old  negatives 
may  be  used,  provided  the  silver  images  be  dissolved  by 
the  familiar  hypo  and  ferricyanide  reducer  or  potassium 
cyanide  solution  and  the  plate  then  well  washed.  The 
gelatinized  glasses  thus  obtained  should  be  soaked  in 
either  the  patent  blue  and  naphthol  green  solution  or 
preferably  in  the  following: 

Brilliant  acid  green  5  g 

Naphthol  green  5  g 

Water  1000  ccm 

Soak  for  thirty  minutes  and  then  rinse  and  dry.  A 
glass  should  also  be  soaked  in  2  per  cent  solution  of 
tartrazin  for  the  same  time,  and  when  dry  the  two 
screens  can  be  bound  up  together  with  paper  in  between 
as  already  advised.  To  make  these  lights  safer  still, 
the  tissue  paper  may  be  soaked  in  the  acid  green  solu- 
tion, or  one  or  two  thicknesses  of  paper  used,  or  even 
thin  blotting  paper  employed. 


THE  DARKROOM  43 

To  those  unaccustomed  to  work  by  green  light  the 
room  will  at  first  appear  very  dark,  almost  black  in  fact, 
but  as  the  eyes  become  accustomed  to  the  light  it  will 
be  found  that  the  illumination  is  quite  sufficient  and 
actually  it  soon  appears  so  bright  that  one  may  get  the 
impression  that  it  is  unsafe.  The  time  needed  for  the 
eye  to  become  accustomed  to  the  light  depends  a  great 
deal  on  the  outside  illumination;  if  one  enters  the  room 
from  a  room  which  is  brightly  lit,  particularly  by  day- 
light, it  may  be  twenty  minutes  or  more  before  full 
vision  is  obtained.  With  use  one  becomes  so  accustomed 
to  the  green  light  that  it  will  be  found  preferable  even 
for  ordinary  negative  work. 

But  now  we  are  in  a  position  to  state  that  even  this 
dim  green  light  is  unnecessary,  as  it  has  been  discovered 
that  certain  of  the  aniline  dyes  possess  the  peculiar 
property  of  desensitizing  the  silver  salts,  so  that  one  has 
only  to  soak  the  plate  in  a  weak  solution  thereof  or  add 
some  dye  solution  to  the  developer,  to  be  able  in  about 
a  minute  to  use  a  bright  yellow  light  for  development, 
and  this  process  in  no  wise  affects  the  image.  The  best 
dyes  for  this  purpose  are  phenosafranin  or  the  ammo- 
nium salt  of  aurantia;  stock  solutions  of  these  dyes 
should  be  made  up,  of  the  phenosafranin  i  :  2000  and  of 
the  aurantia  i  :  1000.  The  former  is  rather  more  effi- 
cient, but  it  has  the  disadvantage  of  staining  the  gela- 
tine deeply.  It  is  also  somewhat  difficult  to  remove,  but 
this  will  be  dealt  with  presently.  For  the  preliminary 
bath  one  part  of  the  phenosafranin  solution  should  be 
diluted  with  nine  parts  of  water,  while  the  aurantia 
solution  should  be  used  full  strength.  In  either  of  the 
solutions  the  plate  should  be  immersed  for  one  minute 
and  can  then,  without  washing,  be  developed  in  the 


44  COLOR  PHOTOGRAPHY 

usual  way.  This  preliminary  soaking  may  be  obviated 
by  the  addition  of  the  dye  solution  to  the  developer, 
hi  the  case  of  the  phenosafranin  at  least.  Ten  per  cent 
of  its  volume  added  to  the  developer  is  as  efficient  as  the 
prior  bath.  As  the  dye  has  to  penetrate  the  gelatine  and 
its  action  is  not  instantaneous,  it  is  obviously  necessary 
to  soak  the  plate  in  the  dye  solution,  or  if  the  dye- 
developer  be  used,  allow  it  to  act  in  a  safelight  for  a 
minute  or  so.  The  soaking  or  initial  development  must 
be  done  first  by  the  ordinary  green  light  or  in  total  dark- 
ness, and  only  after  this  can  the  bright  light  be  used. 
Naturally  also,  as  the  silver  salts  are  not  completely  de- 
prived of  all  sensitiveness,  this  process  must  not  be  abused 
and  the  plate  manipulated  too  near  a  very  strong 
light. 

Suitable  safelights  for  this  method  may  be  made  by 
soaking  two  gelatinized  glasses  in  a  three  per  cent  solu- 
tion of  tartrazin  for  about  fifteen  minutes,  rinsing  and 
drying,  and  then  binding  up  with  tissue  paper.  It 
might  be  preferable  to  soak  the  paper  in  rose  Bengal 
solution,  as  this  makes  a  safer  light,  of  a  bright  pleasant 
orange  color. 

One  further  advantage  of  this  process  is  that  it 
actually  reduces  the  chemical  fog  on  the  negative,  which 
is  a  very  great  assistance  in  practical  work;  for  thus,  in 
common  parlance,  it  enables  us  to  obtain  more  details 
in  the  shadows.  It  also  completely  alters  the  character 
of  the  normal  hydrochinon  developer  which,  as  every 
practical  worker  knows,  has  a  tendency  to  give  hard, 
contrasty  negatives,  whereas  with  the  addition  of  pheno- 
safranin it  works  more  like  metol  or  paramidophenol, 
giving  soft  results.  A  suitable  formula  for  this  modi- 
fication is: 


THE  DARKROOM  45 

A.  Hydrochinon  12  g 
Sodium  sulphite,  dry  50  g 
Potassium  bromide  i  g 
Water  to  1000  ccm 

B.  Potassium  carbonate  50  g 
Phenosafranin,  i  :  2000  solution  200  ccm 
Water  to                                     1000  ccm 

Mix  in  equal  volumes  just  before  use. 

As  stated,  the  phenosafranin  stains  the  gelatine  rather 
deeply  and  this  is  not  readily  washed  out  with  water, 
but  it  can  be  removed  by  treatment  with  either  an  acid 
alum  solution  or  a  nitrite  bath.  The  former  is  made  by 
adding  10  per  cent  of  hydrochloric  acid  to  a  2  per  cent 
solution  of  ordinary  alum,  and  the  nitrite  bath  is  made 
as  follows: 

Sodium  nitrite  i  g 

Hydrochloric  acid  10  ccm 

Water  1000  ccm 

The  best  way  of  using  this  bath  is  to  make  up  a  10  per 
cent  solution  of  the  nitrite;  just  before  it  is  required  for 
use  add  i  part  to  99  parts  of  water  and  then  add  the 
acid;  the  mixed  solution  cannot  be  kept  in  stock.  It 
should  be  noted  that  the  salt  is  nitrite  and  not  nitrate  of 
soda.  The  latter  is  useless,  for  the  efficiency  of  this 
bath  depends  on  the  evolution  of  nitrous  acid,  which 
converts  the  dye  into  a  nitrous  compound,  or  diazotizes 
it.  The  rather  deep  red  stain  is  thus  converted  into  a 
bluish-violet  compound  which  washes  out  from  the  gela- 
tine more  readily.  Naturally,  as  probably  everyone 
knows,  an  acid  bath  should  not  be  used  immediately 
after  fixing  or  the  hypo  is  decomposed,  giving  rise  to 


46  COLOR  PHOTOGRAPHY 

various  sulphur  compounds,  with  the  possible  deposition 
of  sulphur  in  the  gelatine.  Therefore,  the  above  baths 
should  only  be  used  after  the  negatives  have  been 
washed.  The  one  disadvantage  of  the  nitrite  bath  is  the 
evolution  of  nitrous  acid,  which  has  a  rather  unpleasant 
smell  and  in  any  quantity  causes  coughing  and  irritation 
of  the  eyes.  As  the  negatives  have  already  been  fixed, 
the  bath  can  easily  be  used  in  full  daylight,  so  that  one 
need  not  be  cooped  up  in  a  small  dark  room  with  it. 

This  desensitizing  process  is  an  extremely  valuable  one 
and  is  applicable  to  all  sensitive  silver  materials.  With 
bromide  or  development  papers,  aurantia  is  the  only  dye 
that  should  be  used,  as  the  phenosafranin  stains  the 
paper  very  deeply,  while  the  aurantia  can  be  readily 
washed  out. 

It  may  be  as  well  to  add  that  for  the  bright  light  not 
more  than  an  8-candle  power  lamp  should  be  used, 
though  of  course  if  the  work  is  carried  out  at  some  dis- 
tance from  the  lamp  or  an  opaque  screen  be  temporarily 
interposed  between  the  developing  dish  and  the  light,  the 
power  of  the  lamp  may  be  increased. 

As  regards  developers  for  panchromatic  plates  in 
general,  it  is  probable  that  every  worker  has  his  own  pet 
formula,  and  there  is  no  reason  to  alter  it  or  adopt  a 
new  one.  The  two  points  to  be  kept  in  view  in  the  selec- 
tion of  a  developer  are  that  the  negatives  should  be 
what  are  usually  called  "soft,"  that  is,  without  extreme 
contrasts,  and  that  they  should  as  far  as  possible  be  free 
from  fog.  Metol-hydrochinon  appears  to  be  the  favorite 
and  the  following  is  a  standard  formula: 

Metol  4  g 

Sodium  sulphite,  dry  50  g 

Sodium  carbonate,  dry  20  g 


THE  DARKROOM  47 

Hydrochinon  2  g 

Potassium  bromide  o.i  g 

Distilled  water  to  1000  ccm 

For  use  mix  i  part  with  an  equal  volume  of  water.  The 
temperature  of  the  developer  should  be  18°  C.  (65°  F.), 
and  the  duration  of  development  three  to  four  minutes. 
The  author's  favorite  developer  is  the  following: 

A.  Paramidophenol  hydrochloride  30  g 
Sodium  sulphite,  dry  90  g 
Distilled  water  to                              1000  ccm 

B.  Potassium  carbonate  140  g 
Distilled  water  to                                1000  ccm 

For  use  mix  in  equal  volumes.  Temperature  18°  C. 
(65°  F.),  and  duration  of  development  three  and  one 
half  minutes. 

Presumably  everyone  knows  that  the  correct  method 
of  mixing  the  first  formula,  or  any  metol  developer,  is  to 
dissolve  the  metol  in  the  water  and  then  add  the  other 
ingredients  in  the  order  named.  In  making  the  second 
developer,  the  paramidophenol  should  be  dissolved  in 
some  of  the  water,  the  sulphite  in  the  remainder,  and 
the  two  solutions  mixed.  The  paramidophenol  base  is 
thereby  thrown  out  of  solution,  therefore  it  is  essential 
to  thoroughly  shake  the  bottle  before  measuring  a  quan- 
tity for  use.  The  suspended  base  immediately  dissolves 
on  the  addition  of  the  alkali.  It  will  be  noted  that  there 
is  no  bromide  in  this  formula,  and  none  is  required,  as 
the  hydrochloride  combines  with  some  of  the  potash, 
forming  potassium  chloride,  which  is  a  mild  restrainer 
and  fog  preventer.  Should  the  paramidophenol  base 
itself  be  used  instead  of  the  hydrochloride,  and  it  can  be, 
of  course,  with  equally  good  results,  0.05  per  cent  of 


48  COLOR  PHOTOGRAPHY 

potassium  bromide  should  be  added.  Too  much  should 
not  tbe  used,  as  it  actually  slows  the  plate  with  normal 
time  of  development,  that  is,  it  holds  back  the  shadow 
detail,  the  most  important  part  of  the  negative;  if 
development  be  prolonged  sufficiently  to  bring  this  out, 
the  negatives  are,  as  a  rule,  too  hard.  It  may  be  said 
that  if  the  pure  paramidophenol  base  be  chosen,  one 
fourth  less  should  be  used,  that  is,  seventy-five  parts  of 
paramidophenol  will  do  as  much  work  as  one  hundred  of 
the  hydrochloride. 

The  temperature  given  above  for  the  developer  is 
important  and  should  be  strictly  adhered  to.  If  the 
solution  is  cold,  the  development  is  prolonged  and,  con- 
versely, if  it  is  too  warm  the  duration  is  curtailed  and 
there  is  a  much  greater  chance  of  chemical  fog.  Also 
with  strict  adherence  to  a  given  temperature  and  time  of 
development,  the  character  of  all  negatives  will  be  alike. 

Other  developers  may  be  used,  but  enough  has  been 
said  to  enable  the  reader  to  adapt  his  own  pet  formula  to 
the  work.  There  is  one  very  important  point,  which  must 
be  rigidly  observed,  and  that  is  that  the  developer  must 
not  be  used  a  second  time.  If  the  plates  are  so  large  that 
they  cannot  be  developed  together,  which  is  the  ideal 
method,  then  fresh  solution  should  be  used  for  each 
plate;  obviously  there  are  more  possibilities  of  variation 
in  the  negatives  by  separate  development  than  by  devel- 
oping all  together. 

The  reason  why  great  stress  is  laid  upon  this  matter 
of  fresh  solution  for  each  batch  or  each  plate,  is  that 
in  development  the  bromine  set  free  from  the  silver  salt 
by  the  reducing  agent  combines  with  the  alkali  and 
forms  a  bromide,  and  this,  naturally,  in  quantities  vary- 
ing with  the  amount  of  metallic  silver  deposited  to  form 


THE  DARKROOM  49 

the  image;  so  that  one  has,  after  development,  a  solu- 
tion of  unknown  and  variable  bromide  content,  and 
constancy  of  results  is  impossible.  This  may  seem  a 
wasteful  and  expensive  method  of  working;  but  when  one 
considers  the  importance  of  perfect  results,  the  cost  of 
the  fresh  developer  becomes  negligible. 

But  little  need  be  said  about  the  fixing  bath.  Any 
formula  may  be  adopted,  though  an  acid  chrome  bath 
of  the  following  constitution  gives  excellent  results;  it 
fixes  very  rapidly  in  about  five  minutes,  and  hardens  the 
gelatine: 

Sodium  sulphite,  dry  45  g 

Water  100  ccm 

Stir  well  and  add: 

Glacial  acetic  acid  20  ccm 

Then  add  to  the  following,  when  the  hypo  is  dissolved: 

Hypo  400  g 

Hot  water  600  ccm 

Finally  add: 

Chrome  alum  20  g 

Hot  water  50  g 

and  make  the  total  bulk  up  to  1000  ccm. 

The  washing  of  the  negatives  follows  the  usual  course. 
It  is  unnecessary  to  deal  with  intensification  and  reduc- 
tion, as  these  also  can  be  carried  out  as  usual;  but  these 
operations  should  be  avoided  as  far  as  possible  by  cor- 
rect exposure  and  development,  as  the  gradations  are  apt 
to  be  altered  by  them,  with  consequent  false  color- 
rendering. 


CHAPTER  V 
THE  CAMERA  AND  EXPOSURE 

T  TNFORTUNATELY  there  is  no  reasonably  priced 
\J  three-color  camera  on  the  market.  So,  unless  one 
is  prepared  to  make  a  camera,  the  only  alternative  is  a 
sliding  back,  and  this  limits  the  work  in  the  main  to 
subjects  in  which  there  is  no  movement,  as  obviously 
three  successive  and  not  simultaneous  exposures  must  be 
given. 

Many  complicated  forms  of  cameras  have  been  devised, 
with  costly  optical  arrangements  for  obtaining  the  three 
constituent  negatives  with  one  exposure,  but  these  we 
can  ignore.  Possibly  the  simplest  form  of  one-exposure 
camera  is  the  two-step,  of  which  the  best  constructive 
details  were  given  by  C.  E.  K.  Mees,  and  his  instructions 
are  here  followed.  The  camera  was  originally  devised  by 
E.  T.  Butler,  on  the  lines  of  the  photochromoscope  sug- 
gested by  Cros  in  1871.  The  camera  takes  a  seven-inch 
lens,  but  can  be  used  with  any  lens  that  has  not  a 
shorter  focus  than  this.  The  size  of  the  plate  determines 
the  extension  of  the  camera,  and  also  decides  as  to 
whether  the  longer  or  shorter  axis  of  the  plate  is  vertical 
or  horizontal.  The  lens  should  be  one  of  the  newer  anas- 
tigmats  and  work  at  as  large  an  aperture  as  possible, 
for  the  niters  prolong  the  time  of  exposure.  A  reflector 
is  placed  behind  the  lens  at  an  angle  of  45  degrees  to  the 
axis  of  the  lens.  Part  of  the  light  is  reflected  and  passes 
through  a  filter  to  the  plate,  while  the  remainder  which 
50 


THE  CAMERA  AND  EXPOSURE     51 

passes  through  the  first  reflector  meets  a  second  reflector 
placed  parallel  with  the  first.  Here  the  light  is  again 
divided;  the  reflected  part  passes  to  the  second  plate 
through  another  filter,  while  the  rest  of  the  beam  goes 
onward  to  the  third  plate  behind  the  second  reflector. 
It  is  necessary  to  use  the  three  filters,  and  the  images 
must  be  of  identical  size;  in  addition,  the  reflectors 
must  not  give  two  images,  so  that  they  must  be  so  con- 
structed that  the  second  image,  due  to  reflection  from 
the  back  of  the  glass,  is  rendered  harmless. 

All  the  images  have  to  be  in  focus  at  the  same  time, 
and  if  a  black  and  white  object  be  taken  it  must  be 
rendered  of  the  same  value  in  all  three  negatives  Only 
one  kind  of  plate  must  be  used,  that  is,  one  cannot  use 
a  panchromatic  plate  for  the  red  exposure,  an  orthochro- 
matic  for  the  green  and  an  ordinary  for  the  blue.  As 
regards  the  nullification  of  the  double  image  this  can  be 
attained  by  using  colored  reflectors,  and  obviously  this 
can  be  most  satisfactorily  done  by  coating  the  back  of 
the  glass  with  colored  gelatine.  This  coloration  must  be 
the  minus  color  of  the  taking  filter;  for  instance,  in  the 
diagram  (Fig.  10)  it  will  be  seen  that  the  first  reflector, 
which  gives  the  red  record,  is  designated  as  a  "minus 
red  reflector,"  and  a  minus  red  must  be  blue-green. 
In  like  manner  a  minus  blue  must  be  yellow.  It  will  be 
found  that  the  arrangement  suggested  in  the  diagram  will 
be  the  most  satisfactory,  though  the  red  and  green  sen- 
sitive plates  may  change  places.  Then,  of  course,  the 
colors  of  the  back  coatings  of  the  reflectors  must  also  be 
changed,  and  that  for  the  first  reflector  would  be  a  minus 
green,  or  crimson.  Identity  of  size  of  the  images  can  be 
secured  by  altering  the  angle  of  the  reflectors,  as  if  they 
are  raised  the  central  beam  of  light  is  shortened.  The 


S2  COLOR  PHOTOGRAPHY 

reflectors  must  be  separately  adjusted  so  that  the  focus 
of  the  reflected  images  is  the  same  in  each  case,  which 
means  that  the  length  of  the  optical  path  in  glass  must 
be  equal  for  each  plate.  For  this  purpose,  the  thickness 
of  the  filters  must  be  adjusted  so  that  the  length  of  glass 
through  which  each  beam  travels  is  equal.  The  length  of 
the  glass  through  which  the  direct  beam  travels  is  equal 


Lens 


FIG.  10 

to  the  thickness  of  the  two  reflectors  taken  at  an  angle 
of  45  degrees  to  the  axis  of  the  lens.  That  is  to  say,  it 
is  1.41  times  the  actual  thickness  of  the  filters.  The 
thickness  of  the  red  filter  is,  therefore,  equal  to  1.41 
times  the  thickness  of  the  two  reflectors,  while  the 
thickness  of  the  blue  filter  will  be  1.41  times  the  thick- 
ness of  the  yellow  reflector. 

In  order  to  adjust  the  color  of  the  filters  so  that  the 
correct  ratio  may  be  obtained,  pieces  of  film  should  be 


THE  CAMERA  AND  EXPOSURE     53 

placed  between  the  glasses  and  a  black  and  white  chart 
photographed  till  equal  density  results  are  obtained  on 
all  three  plates.  It  will  be  seen  that  the  adjustments 
are  rather  delicate  and  involve  a  considerable  amount  of 
work  by  trial  and  error,  but  this  should  not  deter  anyone 
from  attempting  to  make  such  an  instrument,  as  it  is  the 
cheapest  and  most  convenient  camera  for  a  single  ex- 
posure that  can  be  devised.  It  is  quite  possible  also 
that  a  camera  constructed  on  the  line  of  the  chromo- 
scope,  described  on  p.  125,  would  be  simpler,  though 
not  quite  so  compact.  The  dimensions  are  given  there, 
so  one  can  adapt  it  for  negative  work,  but  as  the  depth 
of  the  instrument  is  lof  inches,  it  obviously  entails  the 
use  of  a  lens  of  focal  length  not  less  than  this,  though 
this  depth  can  obviously  be  cut  down. 

As  an  alternative  to  the  above  described  camera,  the 
following  may  be  adopted.  This  has  some  advantages, 
particularly  as  regards  the  evenness  of  illumination  of 
the  reflected  images,  which  is  frequently  faulty  with 
parallel  reflectors.  This  type  was  patented  in  1896,  and 
some  changes  in  the  disposition  of  the  niters  have  been 
recently  suggested  by  H.  E.  Rendall.  The  internal 
construction  is  shown  hi  the  accompanying  diagram 
(Fig.  n),  in  which  L  is  the  lens  hi  a  focusing  jacket,  or 
obviously  a  short  length  of  bellows  could  be  placed  here. 
A,  the  first  filter,  of  a  mauve  color,  that  is,  one  transmit- 
ting red  and  violet,  is  placed  at  an  angle  of  45  degrees 
to  the  optical  axis  of  the  lens,  and  from  it  some  of  the 
light  is  reflected  to  a  plate  at  PI,  in  front  of  which  is  a 
green  filter  G.  The  remainder  of  the  light  passes  through 
A  and  some  is  reflected  from  B,  a  blue  filter  at  right 
angles  to  A,  to  the  second  plate  P2,  in  front  of  which  is 
an  orange  filter  O.  The  remainder  of  the  light  passes 


54 


COLOR  PHOTOGRAPHY 


through  B  to  P3,  in  front  of  which  there  is  no  filter,  the 
reflector  B  acting  as  filter. 

The  adjustment  of  the  filter  absorptions  is  rather  a 
delicate  matter;  but  a  suitable  filter  for  A  can  be  made 
from  rose  Bengal  0.8  g  per  square  meter,  or  phenosafra- 
nin  0.48  g,  or  a  Wratten  &  Wainwright  No.  31,  minus 
green  i,  may  be  used.  The  G  filter  should  be  the  normal 
tri-color  green  filter,  as  previously  advised.  O  may  be 


FIG.  ii 

made  with  tartrazin  4  g,  or  naphthol  orange  3  g  per 
square  meter;  or  a  Wratten  &  Wrainwright  No.  21, 
monobromofluorescein,  may  be  used.  For  B  a  Wratten 
No.  49b,  C  4  dark,  should  be  used.  Probably  this  filter 
could  be  matched  with  crystal  violet  i  g  and  patent  blue 
1.6  g  per  square  meter;  but  as  these  dyes  cannot  be 
mixed  they  must  be  coated  on  separate  glasses  and 
cemented  together.  Methylene  blue  0.8  g,  or  toluidin 
blue  2  g,  might  take  the  place  of  the  patent  blue;  but 


THE  CAMERA  AND  EXPOSURE     55 

these  do  not  absorb  as  much  violet  as  patent  blue, 
which  has  a  marked  absorption  band  commencing  at 
G  \  H  and  extending  into  the  ultra-violet. 

In  this,  as  in  the  other  camera,  the  optical  paths 
through  glass  must  be  equal,  therefore,  filter  G  must  be 
1.41  times  the  thickness  of  A  plus  1.41  times  the  thick- 
ness of  B,  and  filter  O  must  be  1.41  times  the  thick- 
ness of  A.  A  compensating  filter  must  be  used  on  the 
lens  to  equalize  exposures  and  probably  that  suggested 
for  autochrome  plates  on  p.  143  will  be  very  close  to  the 
ideal. 

One  advantage  of  this  arrangement  of  filters  is  that 
it  gives  the  yellow  image  direct  from  P3,  and  this  forms 
the  basis  for  the  constituent  pictures,  which  is  advan- 
tageous, as  opaque  yellow  pigments  may  be  used  for 
prints.  The  special  advantage  of  the  dark  blue  filter 
is  that  it  cuts  out  some  of  the  violet  and  therefore,  gives 
a  more  brilliant  negative  for  the  yellow.  Naturally  the 
same  arrangement  of  filters  as  advised  for  the  previously 
described  camera  may  be  adopted. 

The  distances  of  the  filters  from  their  respective  plates 
must  be  controlled  in  the  same  way,  that  is,  by  making 
negatives  of  geometrical  figures  and  superposing  them. 
An  expansion  of  the  figures  in  one  negative  will  show 
that  it  is  too  far  from  the  plate,  and  vice  versd. 

The  simplest  form  of  camera  is  undoubtedly  the  semi- 
dialyte.  This  is  dealt  with  elsewhere  (see  p.  222),  and 
also  the  objections  to  this  system. 

With  regard  to  the  lens  that  should  be  used  for  color 
work,  no  special  instructions  need  be  given,  as  any  lens 
may  be  used,  but  some  are  more  suitable  than  others. 
The  newer  anastigmats  are  preferable,  as  they  cover 
sharply  a  given  size  plate  at  a  larger  aperture  than  the 


5  6  COLOR  PHOTOGRAPHY 

older  types,  and  this  is  a  consideration  in  consequence 
of  the  increase  of  exposure  incident  to  the  use  of 
filters. 

Every  plate  maker  gives,  as  a  rule,  the  ratio  of  ex- 
posures for  his  plates  with  a  given  set  of  filters;  but 
this  can  always  be  determined  by  experiment  and  the 
best  method  is  to  use  a  scale  of  greys,  made  by  exposing 
a  piece  of  bromide  paper,  in  geometrical  ratios,  to  white 
light  and  then  developing.  It  is  only  necessary  to  place 
the  edge  of  the  bromide  paper  between  the  edges  of  a 
book,  and  expose  to  white  light  for  say  one  second,  then 
push  the  paper  in  about  half  an  inch  and  give  another 
second  exposure,  then  push  the  paper  further  in  and  give 
two  seconds  exposure,  doubling  the  exposure  in  each  case 
so  that  the  result  will  actually  be  as  follows: 

First  exposure  i  second  =    i 

Second  exposure  i  second  +  (i  already  given)  =    2 

Third  exposure  2  +  (i  +  i)  =4 

Fourth  exposure  4+ (2+1+1)  =8 

Fifth  exposure  8  +  (4  +  2  +  i  +  i)  =  16 

Sixth  exposure  16  +  (8  +  4  +  2  +  i  +  i)  =  32 

This  should  give  six  steps  of  varying  density,  which  will 
be  quite  sufficient  to  determine  the  filter  ratios,  for  one 
has  merely  to  make  three  exposures  through  the  three 
filters  with  this  graduated  strip  as  the  object,  to  obtain 
three  negatives.  A  comparison  of  the  images  will  give 
one  a  very  good  idea  whether  the  ratios  adopted  are  cor- 
rect or  not,  for  if  they  are,  the  scale  of  greys  will  be  alike 
in  all  three  negatives.  If  one  strip  of  the  bromide  paper 
is  shielded  from  all  light,  and  the  other  end  quite  black, 
it  is  easy  to  determine  how  the  exposure  ratios  must  be 
altered  to  attain  equality. 


THE  CAMERA  AND  EXPOSURE     57 

Theoretically,  one  ought  to  determine  the  filter  ratios 
before  each  exposure,  as  the  color  composition  of  day- 
light varies  considerably,  being  very  much  richer  in  red 
and  green  in  sunlight  than  in  shadow  or  in  cloudy 
weather.  But  if  the  filter  ratios  have  been  determined, 
one  may  ignore  this  factor,  at  any  rate  at  first.  The 
actual  exposure  required  without  a  filter  should  be  deter- 
mined by  means  of  one  of  the  exposure  meters  that 
actually  measure  the  chemical  intensity  of  the  light  by 
the  darkening  of  a  paper  to  a  standard  tint.  These  are 
much  more  reliable  than  those  in  which  the  brightness  of 
an  object  is  determined  by  visual  comparison  with  a 
standard;  and  all  tables  based  on  latitude  and  classi- 
fication of  subjects  are  misleading  for  color  photography. 

It  is  extremely  difficult  to  tell  from  a  set  of  negatives 
which  filter  was  used  for  a  particular  negative.  One 
might  imagine  that  this  would  be  an  easy  matter,  but  it 
is  not,  and  even  after  long  experience  it  is  easy  to  be  mis- 
led. It  is,  therefore,  always  well  to  make  the  exposure 
automatically  record  the  filter.  If  the  filters  are  used  in 
contact  with  the  sensitive  surface  this  is  very  easy,  for 
one  has  but  to  affix  to  the  face  of  each  filter,  placed  next 
to  the  sensitive  plate,  an  opaque  letter  designating  the 
color.  When  the  filters  are  used  on  the  lens,  some  little 
device  should  be  thought  out  which  can  be  permanently 
affixed  to  the  plateholders  and  which  will  be  automati- 
cally recorded  by  the  light.  Several  of  these  will  at  once 
suggest  themselves,  such  as  distinct  file  cuts  in  one  edge. 
The  author  has  been  in  the  habit  of  using  small  triangu- 
lar pieces  of  metal  driven  into  the  corners  of  the  front 
of  the  plateholders,  one  piece  in  one,  two  pieces  in  oppo- 
site corners  of  another,  and  none  in  the  third.  There  is 
no  difficulty  in  at  once  picking  out  the  negative  recording 


5  8  COLOR  PHOTOGRAPHY 

each  color,  provided  the  same  holders  are  always  used 
for  the  same  filters,  that  is,  the  one  without  any  corner 
piece  for  the  blue,  that  with  one  for  the  green,  and  that 
with  two  for  the  red,  or  any  other  order  that  is  decided 
upon.  The  corner  pieces  need  not  be  very  large;  a 
right-angled  triangular  piece  measuring  about  5  mm  from 
the  apex  to  the  base  is  quite  large  enough.  This  leads 
to  the  suggestion  that  order  is  a  capital  essential  in  color 
work,  and  that  exposures  should  always  be  made  with  the 
niters  in  one  particular  order,  which  should  be  rigidly 
adhered  to  for  all  time,  as  then  one  does  not  have  to 
think  as  to  whether  one  filter  or  the  other  has  been  used. 
This  particularly  applies  when  separate  exposure  work 
is  undertaken,  and  while  it  may  be  extremely  nice  to  be 
able  to  tackle  any  and  every  subject  that  comes  up  from 
portraits  to  landscapes  and  bric-a-brac,  yet  some  of  the 
most  valuable  work  may  be  done  with  an  ordinary 
camera,  three  separate  plateholders  and  three  exposures, 
confining  one's  work  to  subjects  that  will  not  move,  or 
which  at  least  give  one  time  enough  for  three  separate 
exposures.  As  illustrative  of  this  may  be  mentioned  the 
case  of  a  certain  worker,  who  happened  to  see  the  author 
at  work  on  some  color  prints  and  wanted  to  know  how 
"the  job  was  done."  His  photographic  experience  was 
probably  like  that  of  many  another  amateur;  he  had 
dabbled  in  black  and  white  work  and  had  shot  at  every- 
thing and  anything,  and  then  gotten  rather  tired  of  it 
because  he  had  no  purpose  in  his  work.  He  decided  to 
attempt  color  work,  using  his  old  camera,  with  three 
plateholders  and  three  separate  exposures,  and  his  first 
filters  as  well  as  the  plates  were  borrowed  from  the 
author.  The  only  subject  that  he  could  find  which  was 
sufficiently  brightly  colored  to  satisfy  him  and  would 


THE  CAMERA  AND  EXPOSURE  59 

certainly  not  move,  was  a  somewhat  brilliantly  colored 
old  china  vase.  Curiously  enough,  possibly  another  ex- 
ample of  beginner's  luck,  an  exceedingly  good  result  was 
obtained.  Succeeding  failures  with  landscapes  induced 
our  friend  to  "stick  to  his  pots,"  as  he  expressed  it,  with 
the  result  that  now  he  has  the  finest  collection  of  color 
prints  and  slides  of  old  china  in  the  world  and  has  be- 
come one  of  the  leading  experts  in  that  field,  as  he  was 
led  to  learn  all  that  could  be  learned  about  his  pots. 


CHAPTER  VI 

SUBTRACTIVE  PROCESSES. 
SUPERIMPOSED  CARBON  PRINTS 

PROBABLY  everyone  knows  the  fundamental  basis 
of  the  carbon  process,  a  name  that  has  clung  since 
its  first  inception,  although  carbon  is  no  longer  the  pig- 
ment used.  Briefly,  some  water-insoluble  pigment  is 
suspended  in  gelatine  and  coated  on  paper  somewhat 
thickly;  this  is  then  sensitized  with  a  bichromate  and, 
after  drying,  exposed  to  light  under  a  negative.  Where 
the  light  acts,  the  gelatine  is  rendered  insoluble  in  warm 
water,  so  that  on  treatment  of  such  a  print  with  hot 
water  the  insolubilized  gelatine,  being  undissolved,  re- 
mains to  form  the  image  in  varying  thicknesses  of  gela- 
tine imprisoning  the  coloring  matter.  There  is,  however, 
one  unfortunate  fact,  that,  the  exposure  being  from  the 
front  of  the  tissue,  as  the  pigmented  gelatine  is  called, 
the  insolubilizing  action  proceeds  from  the  surface  down- 
wards, so  that  the  underlying  strata,  those  nearest  the 
paper,  are  still  soluble,  and  will  wash  away  in  the  hot 
water,  leaving  the  surface  image  or  picture  more  or  less 
without  support.  This  action  is  made  clear  from  Fig.  12, 
which  represents  the  tissue  exposed  under  a  strip  nega- 
tive; P  is  the  paper  and  G  the  exposed  gelatine,  the 
amount  of  light  action  being  shown  in  black.  It  is 
obvious  that  only  the  patch  I  on  the  extreme  left  of  the 
diagram  is  anchored  to  the  paper,  where  the  light  action 
has  penetrated  right  through  to  the  support;  in  the  re- 
60 


SUBTRACTIVE  PROCESSES 


61 


maining  patches  there  is  still  an  underlying  stratum  of 
soluble  gelatine  varying  in  thickness  from  II  to  VI.  If 
the  tissues  be  now  immersed  in  hot  water,  this  soluble 
gelatine  will  be  liquefied,  dissolve  in  the  water,  and  leave 


II 


III 


IV 


VI 


FIG.  12 

the  last  five  patches  unsupported  in  any^way,  except 
where  they  are  attached  to  one  another.  Possibly  two 
or  more  might  be  strong  enough  to  hold  thus,  but  the 
lighter  patches,  say  V  and  VI,  would  break  off,  and  these 
represent  the  details  in  the  highlights  of  the  picture. 

To  overcome  this  trouble,  it  is  necessary  to  use  a  tem- 
porary support,  and  squeegee  the  exposed  tissue  to  this 
for  development.  The  condition  hi  this  stage  is  shown  in 
Fig.  13,  in  which  P  as  before  is  the  paper,  G  the  gelatine 


and  T  the  temporary  support.  It  is  obvious  that  the 
patches  II  to  VI  are  now  supported  and  will  not  be  lost 
in  development. 

Three-color  tissues  can  be  obtained  commercially  and 
it  is  not  wise  for  the  amateur  to  attempt  to  make  his 


62  COLOR  PHOTOGRAPHY 

own,  as,  while  the  actual  making  of  the  pigmented  gela- 
tine is  quite  easy,  to  obtain  an  even  thickness  of  coating 
is  not  so.  The  tissue  has  to  be  sensitized  with  bichro- 
mate, and  the  following  is  an  excellent  formula: 

Potassium  bichromate  25  g 

Citric  acid  7  g 

Ammonia  30  ccm 

Water  to  1000  ccm 

This  should  make  a  lemon-yellow  solution,  smelling  dis- 
tinctly of  ammonia.  If  it  does  not  smell,  a  little  more 
ammonia  should  be  added.  The  tissue  should  be  im- 
mersed in  this  for  three  minutes,  and  the  temperature  of 
the  solution  should  preferably  be  15°  C.  (60°  F.);  then 
the  tissue  should  be  placed  between  two  sheets  of  filter 
or  fluffless  blotting  paper,  lightly  rubbed  with  the  hand 
to  remove  excess  solution,  and  hung  up  in  the  dark  to 
dry.  It  does  not  become  light-sensitive  till  dry. 

While  the  time  required  for  this  drying  is  not  a  serious 
matter,  as  tissue  sensitized  in  the  evening  will  be  ready 
for  use  the  next  morning,  yet  by  the  use  of  an  alcoholic 
or  acetone  bath  it  can  be  dried  in  half  an  hour.  For 
this  bath,  however,  it  is  advisable  to  use  ammonium  bi- 
chromate, and,  as  the  alcohol  or  acetone  mixture  will  not 
keep,  it  is  as  well  to  make  a  stock  of  the  ammonium 
solution  as  follows: 

Ammonium  bichromate  25  g 

Distilled  water  to  400  ccm 

When  required  for  use,  mix  ten  volumes  of  this  with 
fifteen  volumes  of  methyl  or  denatured  alcohol,  or  ace- 
tone. Then  pin  the  tissue  on  a  board  by  the  four  cor- 
ners and  paint  the  surface  with  a  broad  flat  brush  satu- 


SUBTRACTIVE  PROCESSES  63 

rated  with  the  spirituous  liquid.  Use  the  brush  first 
lengthwise  and  then  across;  leave  for  five  minutes,  and 
then  paint  again  and  allow  to  dry.  The  brush  should 
not  be  bound  with  metal. 

No  matter  how  the  tissue  has  been  sensitized,  it  will 
not  keep  longer  than  a  week  or  ten  days,  and  it  is  advis- 
able to  use  it  within  three  days. 

The  exposure  has  to  be  judged  by  an  actinometer, 
which  can  be  obtained  from  any  large  dealer. 

Possibly  it  may  be  helpful  to  describe  the  making  of 
an  actinometer,  or  print  meter  as  it  is  sometimes  called. 
Procure  a  pill  box  from  a  drugstore  —  a  one  ounce  box  is 
quite  large  enough  —  place  the  lid,  top  side  down,  on  a 
piece  of  wood,  and  with  a  sharp  penknife  cut  two  parallel 
slits  half  an  inch  long  and  about  a  quarter  of  an  inch 
apart.  Pass  the  knife  blade  through  these  slits  with  a 
little  sideways  pressure  so  as  to  widen  them  sufficiently 
to  allow  a  strip  of  paper  to  pass  freely.  Procure  some 
gelatino-chloride  printing-out  paper,  Solio  or  the  like, 
about  4x5  or  larger,  and  cut  into  strips  just  wide 
enough  to  pass  through  the  slits.  Expose  the  paper  be- 
tween the  slits  to  diffused  daylight  until  of  rather  a  deep 
color,  then  paint  the  top  of  the  lid  with  water  colors 
which  when  dry  will  match  the  color  of  the  paper.  A 
slit  must  also  be  cut  in  the  side  of  the  lid,  parallel  to  and 
in  line  with  the  top  slits,  and  through  this  the  end  of  the 
paper  is  brought,  forming  a  little  tag,  which  enables  one 
to  shift  the  paper  after  exposure. 

To  use  this  actinometer,  the  box  is  placed  by  the  side 
of  the  printing  frame  containing  the  tissue  and  the  nega- 
tive, and  as  soon  as  the  small  exposed  strip  of  paper 
darkens  to  the  standard  tint,  a  fresh  piece  is  pulled  into 
place  and  the  action  of  light  watched  until  the  standard 


64  COLOR  PHOTOGRAPHY 

tint  is  again  reached.  This  operation  is  repeated  as 
many  times  as  necessary.  It  is  usual  to  classify  nega- 
tives according  to  the  number  of  tints  they  require; 
thus  one  speaks  of  a  2-,  4-,  or  y-tint  negative.  Trial 
and  error  will  alone  give  an  idea  as  to  the  number  of 
tints  required;  but  the  average  negative  will  usually  need 
about  five  tints.  By  using  the  long  strips  of  paper,  the 
unexposed  part  can  be  coiled  up  in  the  box. 

Even  more  convenient  than  this  is  a  paper  actinometer 
of  the  so-called  terrace  pattern.  To  make  this,  procure 
a  strip  of  glass;  a  bit  of  an  old  negative  answers  admi- 
rably. This  should  be  one  inch  wide  and  about  six  inches 
long.  Procure  also  some  typewriting  paper;  the  thin 
"onion  skin"  variety  is  excellent.  Cut  this  into  strips 
slightly,  say  one-sixteenth  of  an  inch,  narrower  than  the 
glass  and  of  the  same  length.  Then  arrange  these  strips 
in  step  or  terrace  fashion,  as  shown  in  the  diagram 
(Fig.  14)  in  which  G  represents  the  glass,  and  P  P  a  few 
of  the  paper  strips.  The  width  of  the  steps  is  not  of 
much  importance;  about  three-eighths  of  an  inch  will  be 
6 


P  P 

FIG.  14 

plenty.  This  entails  cutting  a  piece  off  each  strip  and  if 
these  are  laid  one  on  top  of  the  other,  the  result  will  be 
about  sixteen  steps,  each  one  increasing  the  density  by 
one  thickness  of  paper. 

The  steps  should  preferably  be  numbered  or  lettered, 
and  the  numbers  can  be  written  on  a  piece  of  fixed-out 
negative  film  with  waterproof  drawing  ink,  or  may  be 


SUBTRACTIVE  PROCESSES  65 

similarly  written  on  the  paper  itself.  Small  figures  or 
letters  of  ready-gummed  black  paper  may  be  obtained 
commercially.  This  figuring  or  lettering  is  not  absolutely 
essential,  but  it  facilitates  the  reading  of  the  tint  in  prac- 
tice. Finally  a  strip  of  clear  celluloid  should  be  cut  the 
same  length  and  width  as  the  glass,  placed  over  the 
papers,  and  the  whole  bound  up  with  narrow  lantern 
slide  binding  strips,  the  papers  being  pressed  into  as 
close  contact  with  the  glass  as  possible. 

Printing-out  paper  may  be  used  with  this  as  with  the 
other  form;  or  plain  white  paper  may  be  sensitized  with 
the  bichromate  bath  and  used  instead,  and  then  the 
numbers  or  letters  will  appear  yellow  on  a  brown  tinted 
ground.  Such  a  meter  can  be  used  in  a  printing  frame, 
but  another  strip  of  glass  may  be  hinged  to  it  with  cloth 
or  lantern  slide  binding  strip  along  its  length  on  one  side, 
thus  forming  a  little  frame.  A  couple  of  metal  clips 
serve  to  keep  the  paper  in  close  contact  with  the  cel- 
luloid while  printing.  Again,  trial  and  error  must  be  re- 
sorted to,  to  ascertain  the  necessary  exposure;  but,  as  a 
rule,  from  five  to  ten  steps  will  be  sufficient  under  the 
above  conditions.  Of  course,  if  the  paper  selected  be 
thicker,  then  it  will  naturally  stop  more  light  and  not  so 
many  steps  will  be  required. 

Practically  the  carbon  tissue  is  about  the  same  speed 
as  a  print-out  gelatine-chloride  paper;  or  one  can  take 
the  yellow  print  as  a  guide,  as  the  image  can  be  seen  on 
this,  and  when  all  the  details  are  visible  in  the  highlights 
of  this  print,  the  printing  may  be  interrupted.  It  is  as 
well  to  expose  all  three  tissues  at  once,  and  actual  sun- 
light must  not  be  allowed  to  fall  on  the  negatives.  The 
negatives  must  be  provided  with  a  safe-edge,  and  the 
easiest  way  is  to  use  black  lantern-slide  binding  strips. 


66  COLOR  PHOTOGRAPHY 

Stick  them  to  about  half  their  width  on  the  gelatine  of 
each  negative  all  round,  and,  when  the  strip  is  quite  dry, 
shave  off  the  projecting  part  with  a  knife.  The  safe-edge 
prevents  the  tissue  from  washing  up  at  the  edges  during 
development. 

As  the  carbon  prints  are  to  be  developed  on  a  tem- 
porary support  and  subsequently  superimposed  in  regis- 
ter, it  is  necessary  for  this  support  to  be  transparent, 
or  sufficiently  translucent  to  enable  the  outlines  of  the 
images  to  be  seen.  Such  temporary  supports  are  obtain- 
able commercially,  or  celluloid  sheets  ten  one-thousandths 
of  an  inch  thick  may  be  used.  The  temporary  support 
should  be  polished  with  a  solution  of  beeswax  in  tur- 
pentine, such  as: 

Beeswax  20  g 

Resin  20  g 

Turpentine  1000  ccm 

Melt  the  wax  in  a  pot  in  a  water  bath,  add  the  resin, 
preferably  in  powder,  and  finally  add  the  turpentine 
slowly  with  constant  stirring.  Make  a  pad  of  absorbent 
cotton,  wrapped  in  a  piece  of  linen  cloth,  pour  a  little 
of  the  wax  solution  on  the  pad  and  rub  over  the  surface 
of  the  celluloid,  which  can  be  pinned  to  a  board  by  the 
corners;  then  polish  off  the  wax  with  a  cloth.  It  is  as 
well  to  use  two  or  three  clean  pads,  as  but  the  merest 
trace  of  wax  is  required.  Then  hang  up  the  prepared 
sheets  for  twenty-four  hours  to  dry.  Sheet  celluloid  of 
the  given  thickness  can  be  obtained  from  any  dealer, 
either  with  polished  surfaces,  or  one  side  polished  and  the 
the  other  matt.  As  the  final  print  assumes  the  same  sur- 
face as  the  temporary  support,  it  is  thus  possible  to 
obtain  either  matt  or  glossy  pictures.  The  celluloid 


SUBTRACTIVE  PROCESSES  67 

sheets  should  be  obtained  an  inch  larger  each  way  than 
the  tissue,  as  this  facilitates  handling. 

The  exposed  tissue  must  not  be  left  too  long  between 
exposure  and  development,  as  the  insolubilizing  action, 
initially  set  up  by  light,  proceeds  in  the  dark;  so  that  if 
the  exposed  tissue  be  allowed  to  lie  undeveloped  for 
some  hours,  the  final  prints  will  be  actually  darker  than 
they  should  be,  becoming  obviously  overexposed.  The 
exposed  tissue  should  be  immersed  in  a  bath  of  cold 
water  (15°  C.  or  60°  F.),  and  care  taken  that  no  air-bells 
adhere  to  the  surface,  which  can  easily  be  done  by  care- 
fully passing  the  fingers  over  the  surface  both  back  and 
front.  At  first  the  tissue  will  have  a  tendency  to  roll 
itself  up  into  a  spill  with  the  gelatine  side  inside;  then  it 
will  gradually  straighten  itself  out,  and  then  the  edges 
will  turn  back  with  the  paper  inside.  This  is  the  psycho- 
logical moment  to  take  advantage  of.  The  waxed  cellu- 
loid sheet  should  be  slipped  into  the  dish  with  the  waxed 
side  toward  the  gelatine  of  the  tissue,  the  two  brought 
into  contact  under  water,  and  the  print  shifted  until  it  is 
fairly  central;  then  both  should  be  lifted  out,  being  held 
in  contact  by  the  thumbs.  The  two  should  then  be 
placed  on  a  pile  of  paper,  preferably  stout  blotting  paper; 
a  sheet  of  blotting  paper  should  be  placed  over  the  print, 
then  a  sheet  of  ordinary  hard  paper,  and  the  two  thor- 
oughly squeegeed  into  contact;  the  flat  squeegees  are 
better  than  the  roller  type  for  this.  The  print  should 
then  be  placed  between  two  sheets  of  blotting  paper  and 
under  a  moderate  weight,  such  as  a  pile  of  big  and 
heavy  books,  for  about  fifteen  minutes,  and  it  is  then 
ready  for  development. 

The  developer  is  nothing  but  hot  water,  and  it  is  pref- 
erable to  work  at  as  low  a  temperature  as  possible.  A 


68  COLOR  PHOTOGRAPHY 

dish  should  be  filled  with  water  at  38°  C.  (100°  F.),  and 
it  is  advisable  to  have  a  kettle  or  saucepan  with  water 
at  a  higher  temperature,  which  can  be  added  if  the 
temperature  in  the  dish  sinks.  After  about  five  minutes 
the  temperature  of  the  water  in  the  dish  should  be  taken 
with  a  thermometer,  and  if  it  has  cooled  down  too  much, 
which  it  may  do  if  a  thick  stoneware  dish  be  used,  add 
more  hot  water.  Immerse  the  print,  on  its  temporary 
support,  in  the  hot  water,  and  if  any  air  bubbles  adhere, 
break  them  with  the  fingers.  If  the  print  has  been  prop- 
erly exposed,  it  will  be  seen  in  about  two  or  three 
minutes  that  some  of  the  pigmented  gelatine  will  begin 
to  ooze  out  from  under  the  paper.  Then  one  edge  of  the 
paper  should  be  gently  lifted  with  the  finger  nail  and  the 
paper  pulled  off  with  a  gentle  steady  pull;  this  paper  can 
be  thrown  away,  as  it  has  done  its  work.  There  will  be 
no  sign  of  a  picture;  the  face  of  the  celluloid  will  be 
covered  with  a  smeary  mess,  but  if  the  celluloid  be  gen- 
tly moved  about,  to  and  fro  and  up  and  down,  the  solu- 
ble gelatine  will  dissolve  and  the  picture  gradually  make 
its  appearance. 

An  alternative  method  of  working  is,  after  removal  of 
the  paper,  to  slip  a  sheet  of  glass  under  the  celluloid, 
fasten  it  at  two  sides  by  means  of  metal  clips,  and 
immerse  it  face  down,  supporting  it  by  two  glass  or 
metal  blocks  at  each  end,  when  the  soluble  gelatine  will 
sink  away  from  the  face  of  the  print  by  its  own  weight. 
Another  method  is  to  place  one  edge  of  the  glass  bearing 
the  celluloid  face  downwards  in  the  side  of  the  dish  and 
holding  the  other  in  the  fingers  move  the  celluloid  gently 
up  and  down.  Or,  if  a  large  dish  be  used,  the  glass  and 
the  print  may  be  supported  by  one  hand  at  an  angle  of 
about  30  degrees  from  the  horizontal,  and  the  hot  water 


SUBTRACTIVE  PROCESSES  69 

splashed  on  it  with  the  other  hand.  It  is  easy  to  see 
whether  development  is  proceeding  as  it  should  do,  and 
provided  that  the  exposure  is  correct  and  the  tempera- 
ture of  the  water  kept  up,  in  about  five  minutes  the 
print  should  be  finished.  It  may  then  be  placed  face  up 
in  a  dish  of  cold  water,  or  a  very  gentle  stream  of  cold 
water  allowed  to  run  over  it  from  the  tap,  so  as  to  re- 
move any  trace  of  soluble  gelatine  that  may  adhere.  It 
should  then  be  immersed  in  a  5  per  cent  solution  of 
ordinary  alum  for  fifteen  minutes  and  then  put  to  wash 
in  cold  and  frequently  changed  water,  or  gently  running 
water  may  be  used,  and  twenty  minutes  is  long  enough 
for  this.  It  should  then  be  hung  up  to  dry. 

The  developing  dish  should  now  be  well  cleaned  out 
and  the  second  and  third  prints  developed  in  precisely 
the  same  way  as  the  first.  If,  as  soon  as  the  first  print 
is  placed  in  the  cold  water,  the  second  is  developed,  and 
then  the  third  dealt  with  in  the  same  way,  all  three 
prints  can  be  finished  and  in  the  alum  bath  well  within 
an  hour.  One  caution  must  not  be  omitted,  and  that  is 
that  the  print,  until  it  has  dried,  is  very  easily  damaged; 
therefore,  placing  all  three  prints  in  the  same  dish  of 
cold  water  or  alum  solution  should  be  avoided,  other- 
wise some  rough  edge  may  dig  a  piece  out  of  the  tender 
gelatine. 

When  the  prints  are  dry  we  can  proceed  to  transfer 
them  to  their  final  support  in  superposition.  Specially 
prepared  final  supports  are  obtainable  commercially  in 
various  tints,  thicknesses  and  surfaces,  but  only  white 
should  be  used,  any  tint  naturally  affecting  the  color  of 
the  final  picture.  If  the  operator  is  desirous  of  making 
his  own  final  support,  a  sheet  of  bromide  or  developing 
paper  should  be  fixed,  well  washed,  and  immersed  in  10 


7o  COLOR  PHOTOGRAPHY 

per  cent  solution  of  formaldehyde  for  ten  minutes  and 
hung  up  to  dry  without  washing.  At  first  rough  papers 
should  not  be  used,  as  they  are  much  more  difficult  to 
handle  than  the  smooth  kinds. 

The  three  prints  on  their  celluloid  supports  can  be 
temporarily  superimposed,  when  dry,  to  see  whether  any- 
thing like  satisfactory  color-rendering  has  been  obtained. 
If  it  is  sufficiently  pleasing,  the  surface  of  each  print 
should  be  gently  rubbed  over  with  a  pad  soaked  in  ben- 
zol to  remove  any  possible  traces  of  wax  and  again  hung 
up  to  dry.  As  the  benzol  is  very  volatile,  this  will  only 
take  a  few  minutes.  Meanwhile  immerse  a  sheet  of  the 
final  support,  which  should  always  be  larger  than  the 
print,  in  a  dish  of  cold  water  and  allow  it  to  soak  for  at 
least  half  an  hour  (an  hour  is  not  too  long);  this  is  to 
give  the  paper  fibers  a  chance  to  fully  expand. 

A  cement  is  required  to  make  the  prints  stick  together; 
a  plain  6  per  cent  solution  of  gelatine  may  be  used,  or 
the  following  may  be  made  up  and  will  keep  well  in  a 
corked  bottle: 

Soft  gelatine  10  g 

Glacial  acetic  acid  10  ccm 

Distilled  water  480  ccm 

Allow  to  soak  for  about  half  an  hour  and  then  melt  in  a 
water  bath  and  add: 

Methyl  or  denatured  alcohol  500  ccm 

Phenol  (carbolic  acid)  10  ccm 

This  cement  must  be  melted  by  heat  each  time  before 
using  and  should  be  applied  rather  thinly  with  a  broad 
flat  brush. 


SUBTRACTIVE  PROCESSES  71 

The  yellow  print  should  be  immersed  in  cold  water 
for  ten  minutes,  then  brought  into  contact  with  the 
soaked  final  paper,  lifted  out  together  with  this,  thor- 
oughly squeegeed,  and  hung  up  to  dry.  When  quite  dry 
the  temporary  support  of  celluloid  may  be  stripped  off, 
leaving  the  print  on  the  paper.  This  print  should  now 
be  pinned  to  a  board  by  the  corners,  and  the  blue  print 
on  its  support,  which  may  have  the  corners  cut  off  to 
allow  room  for  the  pins  of  the  yellow  print,  should  be 
placed  on  top  and  the  two  shifted  about  until  accurate 
register  is  obtained,  and  two  more  pins  driven  through 
the  two  supports;  the  top  support  bearing  the  blue  im- 
pression should  then  be  lifted  up  and  the  yellow  print 
quickly  painted  with  the  cement,  which  must  not  be  too 
hot,  and  the  blue  print  then  lowered  into  place.  Pos- 
sibly some  little  shift  may  be  necessary,  but  it  should  not 
be;  anyway,  one  can  examine  the  register  with  a  magni- 
fying glass.  When  satisfactory,  the  two  should  be  hung 
up  to  dry  and  the  celluloid  stripped  as  before.  The 
third,  the  red  impression,  is  superimposed  in  the  same 
way.  It  should  be  noted  that  the  pins  referred  to  above 
are  the  glass  headed  push-pins,  and  if  these  be  driven 
with  steady  straight  pressure  through  the  supports,  there 
is  very  little  tendency  for  the  prints  to  shift. 

Another  process,  which  while  actually  a  carbon  pro- 
cess, employs  no  light  for  the  insolubilization  of  the  gela- 
tin, relying  upon  the  action  of  finely  divided  silver  on 
the  bichromates,  which  causes  insolubilization  of  gelatine 
in  which  the  silver  is  imbedded,  is  known  as  the  Raydex 
process.  This  peculiar  action  of  silver  on  the  bichro- 
mates was  discovered  by  Howard  Farmer  in  1889,  and 
for  years  lay  dormant,  no  practical  application  of  it 
being  made.  Briefly  the  process  is  as  follows;  the  three 


7  2  COLOR  PHOTOGRAPHY 

constituent  negatives  are  obtained  in  the  usual  way  and, 
from  these,  prints  are  made  on  a  special  bromide  paper. 
These  prints  are  immersed  in  water  and  brought  into 
contact  with  the  colored  pigmented  tissue  which  has  been 
previously  soaked  in  some  special  solutions,  where  they 
are  left  for  a  short  time.  The  print  is  then  separated 
from  the  tissue,  which  is  squeegeed  to  a  temporary  sup- 
port, developed  with  warm  water  and  then  superimposed 
in  register  as  described  above  for  straight  carbon  work. 
The  actual  formula  for  the  solution  has  never  been  pub- 
lished, but  in  all  probability  it  is  a  compound  of  cupric 
sulphate  and  bichromate.  The  instructions  issued  by  the 
Raydex  Company  may  be  summarized  as  follows:  from 
the  three  constituent  negatives  three  prints  must  be 
made  on  the  special  bromide  paper,  giving  the  same  ex- 
posure to  each;  to  get  the  correct  exposure,  make  a  trial 
print  from  the  negative  taken  through  the  green  filter. 
The  exposure  required  to  obtain  a  rich  black,  with  clear 
highlights,  and  which  will  develop  out,  that  is,  to  a  point 
where  on  continuing  development  no  apparent  further 
action  takes  place,  is  the  correct  exposure  for  the  three 
negatives.  Development  should  not  be  too  rapid,  as 
this  gives  weak  colors.  Wet  the  three  exposed  prints  and 
develop  side  by  side  with  any  good  metol-hydrochinon 
developer.  After  development,  transfer  without  washing 
to  an  acid  fixing  bath  for  at  least  ten  minutes  and  then 
wash  thoroughly  and  dry,  or  use  at  once  for  making  the 
color  prints. 

Three  transparent  supports  must  be  waxed  at  least 
half  an  hour  before  use.  Soak  the  bromide  prints  in 
water  and  when  limp  place  them  face  upwards  on  clean 
glasses  (old  negative  glasses  are  suitable).  The  prints 
should  be  trimmed  smaller  than  the  color  sheets.  The 


SUBTRACTTVE  PROCESSES  73 

back  of  the  yellow  color  sheet  is  slightly  damped  and 
then  immersed  for  two  minutes  in  a  special  solution, 
then  rinsed  and  placed  on  top  of  the  correct  bromide 
print  under  the  surface  of  water,  lif ted  out  and  squeegeed 
into  contact,  and  set  aside  for  twenty  minutes,  when  the 
action  is  complete.  The  same  procedure  is  gone  through 
with  the  blue  and  the  red.  The  color  sheets  should  be 
trimmed  to  within  about  one-eighth  of  an  inch  of  the 
size  of  the  bromide  prints  and  then  the  pah's  pulled 
apart.  Squeegee  the  color  sheets  into  contact  with  the 
dry  waxed  supports  and  allow  to  remain  for  ten  minutes, 
develop  in  water  from  43°  to  49°  C.  (100°  to  no°F.), 
and  when  development  is  complete  rinse  in  clean  water 
at  38°  C.  (90°  F.),  and  hang  up  to  dry.  The  bromide 
prints  after  washing  can  be  redeveloped  and  again  used. 
Single  transfer  paper  is  soaked  in  water  for  half  an  hour, 
and  the  yellow  print  squeegeed  thereon  and  dried.  The 
blue  and  red  prints  are  painted  with  a  special  liquid 
cement  and  dried.  When  the  paper  and  the  yellow  print 
are  perfectly  dry  the  paper  is  stripped,  and  the  surface 
freed  from  wax  by  treatment  with  benzol.  The  blue 
print  on  its  transparent  support  should  be  soaked  in 
water  for  a  few  minutes  with  the  yellow  print  and  the 
two  brought  into  contact,  lifted  out  and  lightly  squee- 
geed into  contact  and  dried.  When  dry  treat  with  benzol 
and  transfer  the  red  print  in  the  same  way.  The  prints 
are  reversed  but  for  many  purposes  this  will  be  of  no 
moment.  An  alternative  process  is  given,  in  which  the 
prints  are  produced  on  glass  and  stripped  with  hydro- 
fluoric acid,  but  this  seems  rather  tedious.  It  will  be 
seen  that  the  process  is  in  its  essentials  the  carbon  pro- 
cess pure  and  simple,  with  the  important  modification 
that  the  light  exposure  is  eliminated.  Some  excellent 


74  COLOR  PHOTOGRAPHY 

results  are  possible  by  this  method.  The  fact  of  being 
able  to  make  the  carbon  prints  at  night  is  a  great  advan- 
tage, and  also  that  having  once  gotten  good  bromide 
prints  almost  any  number  of  duplicate  color  prints  can 
be  made  from  them. 


CHAPTER  VII 
THE  IMBIBITION  PROCESS 

THIS  process  is  the  transfer  of  a  dye  image  to  a  gela- 
tine film;  as  the  result,  prints  are  formed  consist- 
ing only  of  transparent  aniline  dyes  in  a  single  layer  of 
gelatine.  The  finished  pictures  are  very  luminous  and 
rich  in  coloring.  There  are  various  methods  by  which 
this  result  can  be  obtained;  either  by  using  a  primary 
gelatine  relief,  staining  this  up,  and  using  as  the  dye 
matrix,  or  by  using  the  property  that  hardened  gelatine 
possesses  of  not  absorbing  certain  dyes,  and  the  fact  that 
these  dyes  will  migrate  or  wander  into  another  gelatine 
film. 

Practically,  one  may  liken  the  relief  processes  to  the 
use  of  a  rubber  stamp,  which  temporarily  takes  up  the 
coloring  matter,  only  to  give  it  up  when  pressed  against 
an  absorbing  support. 

The  pinatype  process  was  originally  suggested  by 
Edwards  in  1875,  and  independently  by  Cros  in  1881, 
and  was  introduced  commercially  by  Meister,  Lucius  & 
Briining  in  1906.  The  original  process,  as  suggested  by 
the  last-named  firm,  required  the  three  original  nega- 
tives, three  transparencies  from  the  same  and  three 
print-plates,  which  were  prepared  from  the  transpar- 
encies by  exposure  of  bichromated  gelatine  plates;  it 
will  thus  be  seen  that,  exclusive  of  the  negatives,  six 
plates  were  required  before  a  single  print  was  possible. 
But  equally  good  results  can  be  obtained  by  using  the 
transparencies  themselves  as  print-plates,  thus  saving 

75 


7  6  COLOR  PHOTOGRAPHY 

one  step  in  the  process;  this  modification  was  suggested 
by  Didier,  the  actual  inventor  of  the  process. 

The  following  is  the  method  of  making  the  bichro- 
mated  print-plates.  It  is  assumed  that  the  three  constit- 
uent negatives  have  been  secured  and  that  ordinary 
silver  transparencies  have  been  made  from  them.  As 
regards  these  last,  the  only  comment  necessary  is  that 
they  should  not  be  too  hard  and  should  partake  rather 
of  the  character  of  negatives  than  of  brilliant  lantern 
slides.  The  bichromated  plates  can  be  prepared  with: 

Hard  gelatine  50  g 

Ammonium  bichromate  20  g 

Water  1000  ccm 

The  gelatine  should  be  cut  up  into  small  pieces  and  soaked 
in  the  water  for  about  thirty  minutes  and  then  melted 
by  the  aid  of  heat,  the  bichromate  added  and  the  mix- 
ture filtered,  while  hot,  through  Canton  flannel  or  two 
or  three  thicknesses  of  linen.  The  quantity  of  this  mix- 
ture should  be  400  to  500  ccm  for  every  square  meter  of 
glass.  The  preparation  of  the  solution  and  the  coating 
of  the  glass  can  be  performed  by  weak  daylight  or  arti- 
ficial light.  The  glass  can  be  old  negative  glasses,  well 
cleaned  and  polished.  They  should  be  placed  on  a  leveled 
slab  and  the  requisite  quantity  of  the  gelatine  mix- 
ture poured  on  them  and  coaxed  out  to  the  edges.  It 
will  be  found  that  a  pipette  is  the  most  handy  tool  for 
this,  and  the  temperature  of  the  solution  may  be  about 
55°  C.  (130°  F.).  As  soon  as  the  gelatine  has  firmly  set, 
the  plates  can  be  racked  for  drying,  and  the  remarks 
already  made  as  to  this  operation  in  the  case  of  filters 
and  plate  sensitizing  apply  here  also.  The  plates  must 
be  dried  in  the  dark.  A  possible  variation  of  this  proc- 


THE  IMBIBITION  PROCESS  77 

ess,  and  one  that  may  commend  itself,  is  to  omit  the 
bichromate  salt  from  the  above  formula  and  coat  a  stock 
of  glass  with  plain  gelatine  solution;  sensitize  this  as  re- 
quired by  immersion  in  plain  bichromate  solution,  about 
5  per  cent,  then  rinse  and  dry.  By  this  method  there  is 
naturally  less  chance  of  the  plates  spoiling. 

In  either  case  the  bichromated  plates  are  exposed 
under  the  transparencies  to  daylight,  and  as  in  the  car- 
bon process,  an  actinometer  should  be  used;  but  it  will 
be  possible  to  do  without  this,  as  the  image  is  easily  seen 
in  a  brown  color  against  the  bright  yellow  ground.  The 
exposure  should  be  such  that  the  image  is  visible  in  all 
its  details,  even  in  the  high-lights.  After  exposure,  the 
plates  are  soaked  in  cold  water  until  the  drainings  are 
colorless,  or,  if  time  is  a  consideration,  the  plates  may  be 
immersed  in  a  10  per  cent  solution  of  sodium  bisulphite 
until  colorless  and  then  washed.  Though  not  absolutely 
necessary,  it  is  advisable  to  let  them  dry  then,  but  before 
this  they  should  be  immersed,  just  for  a  minute  or  two, 
in  their  respective  dye  baths,  as  this  enables  one  to  tell 
which  plate  is  which.  Otherwise  it  is  extremely  difficult 
to  distinguish  them,  as  the  image  is  almost  invisible. 

The  alternative  process,  in  which  the  silver  transpar- 
encies are  used  as  the  print-plates,  is  to  be  preferred,  as 
the  films  are  actually  harder.  The  transparencies  must 
be  somewhat  denser  than  for  the  last  process  and  have 
absolutely  clean  whites,  and  it  is  important  not  to  use 
any  developer  that  has  a  tanning  action  on  the  gelatine. 
The  transparency  for  the  yellow  impression  should  be 
sensitized  in: 

Ammonium  bichromate  12.5  g 

Ammonia  100  ccm 

Distilled  water  1000  ccm 


7  8  COLOR  PHOTOGRAPHY 

Those  for  the  blue  and  red  are  bathed  in: 

Ammonium  bichromate  20  g 

Ammonia  200  ccm 

Distilled  water  1000  ccm 

The  plates  should  be  immersed  for  five  minutes  and  then 
dried.  Before  exposure,  the  backs  of  the  plates  must  be 
thoroughly  cleaned,  as  any  dirt  would  show  in  the  result 
as  a  darker  patch.  They  are  placed  in  an  ordinary  print- 
ing frame,  gelatine  side  inside,  and  in  contact  with  the 
gelatine  should  be  placed  a  sheet  of  printing-out  paper, 
which  acts  as  an  actinometer.  The  insolation  is  carried 
on  until  the  details  appear  in  the  shadows,  and  naturally 
this  image  is  a  negative;  the  yellow  plate  requires  about 
double  the  exposure  of  the  others.  After  exposure,  the 
plates  should  be  well  washed,  or,  to  shorten  the  time, 
may  be  immersed  in  the  bisulphite  solution  recommended 
above,  or  in  a  5  per  cent  ammonia  solution. 

The  transparencies  are  then  ready  for  staining  up,  but 
as  the  presence  of  the  black  silver  image  makes  it  diffi- 
cult to  see  the  dye  image  in  the  subsequent  superposi- 
tion, it  is  advisable  to  dissolve  the  silver  with  weak  hypo 
and  ferricyanide.  This  process  not  only  presents  the 
advantage  of  cutting  out  the  making  of  the  print-plates, 
but  the  correct  exposure  can  be  easily  determined.  The 
plates  are  very  hard,  and  will  stand  subsequent  treat- 
ment without  damage.  In  consequence  of  the  feeble  re- 
lief, the  prints  show  a  most  delicate  detail;  and  the  suc- 
cessive prints  are  very  regular  owing  to  the  superficial  film 
being  backed  up  by  the  insoluble  film  caused  by  the  ex- 
posure through  the  back. 

The  dyes  that  should  be  used  for  this  process  are  natu- 
ral carmine  or  lanafuchsin  BB  or  SL  for  the  red  impres- 


THE  IMBIBITION  PROCESS  79 

sion,  indulin  blue  for  the  blue,  and  acid  yellow,  mikado 
yellow,  or  quinoline  yellow  for  the  yellow.  The  dyes  are 
made  up  in  three  per  cent  solutions  in  distilled  water; 
but  if  the  carmine  be  used,  then  4  g  should  be  rubbed  up 
into  a  paste  with  a  little  water,  and  ammonia  added  drop 
by  drop  until  a  perfectly  clear  deep  red  solution  is  ob- 
tained. About  5  ccm  of  the  ammonia  will  be  required, 
and  then  water  should  be  added  to  make  the  solution  up 
to  100  ccm  and  it  will  be  ready  for  use. 

As  was  pointed  out,  the  printing  colors  are  the  comple- 
mentaries  of  the  filter  colors,  and  this  applies  to  all  sub- 
tractive  processes,  so  no  further  mention  of  this  will  be 
made.  The  first  time  of  staining,  the  plates  will  require 
about  twenty  minutes  to  attain  full  intensity;  but  in 
subsequent  staining  only  about  ten  minutes.  The  print- 
plates  may  be  used  for  an  almost  indefinite  number  of 
pulls;  exactly  how  many  has  never  been  determined, 
this  naturally  being  dependent  on  the  care  with  which 
they  are  used. 

It  is  actually  immaterial  in  what  order  they  are  pulled; 
but  it  will  be  found  easier  to  make  the  order  blue,  red, 
yellow  or  red,  blue,  yellow.  The  reason  for  this  is  that 
it  is  much  easier  to  obtain  registration  of  the  outlines  of 
objects  in  one  of  these  series  than  if  the  yellow  be  put 
down  first,  for  this  looks  so  faint  against  the  white  paper 
that  it  is  not  easy  to  secure  accurate  registration  of  the 
outlines.  After  repeated  use,  the  print-plates  become 
deeply  stained  even  in  the  whites,  and  while  this  is  no 
disadvantage  in  practice  as  regards  the  dyes  transferring, 
it  is  a  great  disadvantage  from  the  point  of  view  of  easy 
registration,  as  it  makes  it  difficult  to  discern  the  outlines 
of  the  objects.  When  this  occurs,  the  plate  should  be 
immersed  in  a  bath  of: 


8o  COLOR  PHOTOGRAPHY 

Potassium  permanganate  2  g 

Sulphuric  acid,  10  per  cent  solution  10  ccm 

Distilled  water  1000  ccm 

As  soon  as  the  dye  has  bleached  out,  the  plate  should  be 
immersed  in  a  five  per  cent  solution  of  sodium  bisulphite 
until  all  brown  stain  disappears,  and  then  well  washed. 

The  paper  to  which  the  dye  image  is  transferred  is 
plain  gelatine-coated  paper,  and  this  gives  one  a  wide 
choice  of  surfaces.  One  can  easily  obtain  a  suitable 
paper  by  fixing  out  bromide  or  developing  paper,  wash- 
ing and  treating  with  five  per  cent  solution  of  formalde- 
hyde for  ten  minutes,  and  drying  without  washing. 
After  the  print-plate  has  been  soaked  in  the  dye  solution 
for  a  sufficient  time,  it  should  be  rinsed  with  water  until 
the  drainings  are  practically  colorless.  A  sheet  of  paper 
should  be  soaked  in  water  for  about  five  minutes,  left 
for  half  a  minute  after  the  surface  moisture  has  been 
blotted  off,  then  the  print-plate  squeegeed  down  and  the 
two  left  in  contact.  The  paper  should  be  uppermost,  a 
thin  piece  of  wax  paper  placed  over  it  and  the  squeegee 
used  well,  stroking  from  the  middle  of  the  print  out  to 
the  sides;  roller  squeegees  are  not  so  suitable  for  this 
as  the  old  fashioned  flat  ones.  The  paper  and  plate 
should  be  left  in  contact  for  about  fifteen  minutes,  and 
then  a  small  corner  of  the  paper  turned  back  and  the 
image  examined  to  see  if  it  is  deep  enough.  Naturally, 
a  little  experience  is  required  to  tell  this,  but  one  soon 
becomes  expert  enough.  If  the  pull  is  not  thought  suffi- 
ciently intense,  the  corner  must  be  squeegeed  down  again 
and  the  whole  left  a  little  longer,  and  again  examined. 

The  next  plate  is  treated  as  described  for  the  first,  but 
as  at  first  one  is  a  little  awkward  in  obtaining  register, 


THE  IMBIBITION  PROCESS  81 

a  piece  of  thin  celluloid  is  placed  over  the  first  pull.  The 
thinnest  celluloid  that  can  be  obtained  should  be  used, 
and  creases  or  folds  in  this  should  be  avoided;  the  cellu- 
loid should  be  cut  about  an  inch  longer  than  the  print, 
as  this  gives  one  a  convenient  handle  to  catch  hold  of, 
and  it  should  be  placed  over  the  first  print  so  that  a  little 
space  is  left  at  the  top  of  the  print  with  no  celluloid. 
The  idea  is  that  this  space  enables  one  to  temporarily 
clip  or  hold  the  second  plate  in  contact  with  the  print, 
after  registration  has  been  obtained,  and  then  withdraw 
the  celluloid  without  shifting  the  relative  positions  of  the 
second  print-plate  and  the  paper.  The  easiest  way  to 
work  is  to  form  a  temporary  desk  by  supporting  a  piece 
of  thick  glass  on  two  piles  of  books  or  blocks  of  wood, 
and  place  under  this  a  mirror  or  white  card  that  will  re- 
flect the  light  through  the  paper  and  the  second  plate. 
Then,  with  a  magnifying  glass,  it  will  be  found  fairly 
easy  to  obtain  coincidence  of  the  outlines.  Then,  if  the 
plate  and  the  paper  are  firmly  held  at  the  top,  the  cellu- 
loid may  be  slipped  out  and  the  two  well  squeegeed 
together. 

The  third  print  is  obtained  in  exactly  the  same  way  as 
just  described.  Under  no  circumstances  must  the  one 
pull  be  allowed  to  dry  before  the  next  impression  is 
superimposed.  Therefore,  it  may  be  as  well  to  place  the 
print-plate  with  the  adherent  paper  between  sheets  of 
stout  blotting  paper  well  dampened  with  water. 

Working  in  this  way,  particularly  if  the  gelatined 
paper  has  been  well  hardened  with  formaldehyde,  there 
is  but  little  danger  of  want  of  exact  register  from  expan- 
sion or  shrinkage  of  the  paper.  Only  in  the  case  of  very 
soft  paper  stock  is  there  any  danger.  In  such  cases,  the 
paper  should  be  soaked  in  water  for  at  least  half  an  hour 


82  COLOR  PHOTOGRAPHY 

before  making  the  first  pull.  A  still  more  radical  remedy 
is  to  pin  the  paper  with  the  gelatine  side  down  on  a 
board,  and  paint  the  back  with  a  celluloid  varnish, 
such  as: 

Scrap  celluloid  20  g 

Amyl  acetate  50  ccm 

Acetone  45°  ccm 

Methyl  alcohol  to  1000  ccm 

Two  or  three  coats  of  this  thinly  applied  will  prevent 
any  expansion  or  contraction.  The  paper,  after  this 
treatment,  must  be  left  at  least  twenty-four  hours  to 
thoroughly  dry. 

If,  when  the  three  impressions  are  pulled  in  super- 
position, it  is  found  that  one  or  other  color  predominates, 
and  of  course  the  depth  of  the  staining  is  dependent  on 
the  time  of  contact  between  the  paper  and  the  plates, 
one  of  the  plates  may  be  again  soaked  in  the  dye  solu- 
tion and  again  superimposed  in  register  and  left  for  a 
short  time.  Thus  the  excess  of  red  may  be  killed  by 
a  second  staining  up  with  blue,  and  excess  of  blue  by  a 
second  staining  up  with  yellow  or  red.  If  the  whole 
picture  is  too  weak,  all  three  plates  may  be  reapplied. 
If  it  is  too  dark,  it  may  be  moistened  in  water  and  squee- 
geed in  contact  with  a  gelatine  coated  plate  for  a  short 
time,  and  some  of  the  excess  dye  will  migrate  into  this 
plate.  A  negative  must  not  be  used  for  this,  as  the  sil- 
ver image  prevents  the  even  transfer  of  the  dye,  but 
naturally  a  plate  with  the  silver  removed  can  be  used, 
and  by  careful  and  frequent  examination  of  the  corner  of 
the  print  as  already  advised,  one  can  soon  tell  when  the 
reduction  has  proceeded  far  enough. 

The  prints  thus  obtained  are  sufficiently  permanent  to 


THE  IMBIBITION  PROCESS  83 

withstand  months  of  exposure  to  any  daylight  that  may 
be  met  with  hi  an  ordinary  room;  but  they  may  be 
made  more  permanent  by  five  minutes  immersion  in  a 
three  per  cent  solution  of  cupric  sulphate.  This  turns 
the  reds  into  a  more  violet  hue,  and  it  is  hardly 
necessary. 


CHAPTER  VIII 
RELIEF  PROCESSES 

HOWARD  FARMER  discovered   that  if  a  silver 
image  imbedded  in  gelatine  was  immersed  in  a  solu- 
tion of  a  bichromate  a  reaction  took  place  and  the  bi- 
chromate was  reduced,  so  that  the  gelatine  surrounding 
each  minute  particle  of  silver  became  insoluble  in  hot 
water.    On  this  has  been  based  a  process  for  obtaining 
a  gelatine  relief,  which  can  be  stained  up  and  used  as  the 
matrix  for  the  transfer  of  dyes  to  gelatined  paper.    This 
is  obviously  the  same  principle  as  that  involved  in  the 
carbon  process,  with  the  added  advantage  of  being  inde- 
pendent of  daylight.    Obviously  it  suffers  from  exactly 
the  same  disadvantage,  that  is,  if  we  expose  from  the 
front  in  the  usual  way,   the  delicate  details  and  half 
tones  will  be  unsupported  and  will  wash  away  in  the 
development.     We  must,    therefore,  print  through  the 
back  of  the  support.    In  the  case  of  celluloid  this  is,  of 
course,  of  no  moment,  as  the  thickness  of  the  celluloid 
is  not  sufficient  to  make  the  image  markedly  diffuse; 
but  if  it  is  desired  to  use  glass  plates,  the  thickness  of 
the  glass  causes  want  of  sharpness  in  the  print.    This 
may  not  be  sufficient  to  be  objectionable  to  some  people 
but  unless  the  glass  of  all  three  plates  is  of  exactly  the 
same  thickness,  the  diffusion  of  the  images  will  differ 
and   the   individual   pulls   be   unequally   sharp.     This 
trouble  in  using  glass  plates  may  be  gotten  over  by 
making  the  positives  in  the  camera  by  copying,  as  is 
84 


RELIEF  PROCESSES  85 

done  when  making  lantern  slides,  only  the  transparency 
plate  must  be  placed  with  its  glass  towards  the  lens  and 
allowance  for  its  thickness  made  in  focusing  the  image. 

In  the  case  of  celluloid  films,  while  the  same  procedure 
may  be  adopted,  one  can  print  by  contact,  using  an 
electric  lamp.  An  opaque  card  with  an  aperture  about 
one  inch  in  diameter  cut  in  it  may  be  placed  over  the 
bulb,  with  a  ground  glass  covering  the  hole,  so  as  to  ob- 
tain diffused  light.  The  lamp  should  be  placed  four  or 
five  feet  from  the  printing  frame.  The  exposure  under 
these  conditions  is  naturally  longer  than  in  contact 
printing,  but  it  is  not  unduly  prolonged. 

Any  slow  transparency  plate  may  be  used,  but  con- 
trast or  photomechanical  plates  should  be  avoided,  as 
they  readily  give  too  much  contrast.  Any  developer 
except  pyrogallol  may  be  used,  and  this  should  be 
avoided  on  account  of  its  tanning  action  and  staining. 
The  images  should  not  be  too  dense,  otherwise  the  pull 
from  the  matrix  may  be  wanting  in  details  in  the  high- 
lights. Naturally  the  positive  must  also  be  free  from  fog, 
for  as  the  gelatine  is  rendered  insoluble  wherever  there 
is  silver,  and  fog  is  nothing  but  silver  generally  distrib- 
uted, it  might  happen  that  the  fog  is  sufficiently  bad  to 
give  insoluble  gelatine  and  consequently  color  where  it 
is  not  wanted. 

The  positive  should  preferably  be  fixed  and  washed 
as  usual,  though  this  is  not  absolutely  essential,  and  then 
immersed  in  one  of  the  following  baths: 

Chromic  acid  5  g 

Potassium  bromide  20  g 

Water  1000  ccm 
or: 


86  COLOR  PHOTOGRAPHY 

Potassium  bichromate  6  g 

Hydrochloric  acid  10  ccm 

Water  1000  ccm 

These  may  be  used  over  and  over  again,  in  fact  until 
their  action  gets  too  slow;  they  should,  however,  be  kept 
in  the  dark,  when  not  in  use. 

The  positive  should  be  immersed  in  the  solution  in  a 
dish,  and  the  dish  rocked  until  it  is  seen  that  it  is 
bleached  quite  through  to  the  back,  on  looking  through 
the  glass.  Prolonging  the  immersion  does  no  harm,  but 
as  a  rule  ten  minutes  is  sufficient  for  any  positive,  no 
matter  how  dense  it  may  be.  The  bleached  positive  is 
then  immersed  in  water  at  about  40°  C.  (105°  F.),  when 
the  gelatine  will  be  seen  to  gradually  dissolve  away, 
leaving  the  whitened  silver  image,  which  is  either  the 
bromide  or  chloride.  Should  the  gelatine  not  dissolve 
easily,  the  temperature  of  the  water  may  be  raised  two 
or  three  degrees;  but  it  is  not  advisable  to  force  develop- 
ment, as  otherwise  some  of  the  isolated  patches  and  the 
fine  details  may  be  washed  away.  The  plate  should 
then  be  rinsed  in  cold  water  to  remove  any  adherent 
soluble  gelatine,  washed  to  remove  any  traces  of  the  bi- 
chromate-acid bath,  which  would  decompose  the  fixing 
bath,  and  immersed  in  a  hypo  bath  until  the  white  sil- 
ver salt  is  dissolved.  After  this  it  requires  but  a  brief 
washing,  and  can  be  dried  or  immediately  stained  up. 

The  author  has  a  fancy  for  immediately  staining  up 
lightly,  as  this  prevents  any  subsequent  mistake  as  to 
which  plate  is  which,  as  otherwise  when  dry  the  relief  is 
so  slight  that  it  is  difficult  to  distinguish  between  the 
various  plates.  The  dyes  used  may  be  the  same  as  those 
suggested  for  the  pinatype  process,  the  final  transfer 


RELIEF  PROCESSES  87 

paper  may  be  treated  in  the  same  way,  and  the  method 
of  superposition  of  the  images  also  followed. 

Exactly  how  many  pulls  may  be  taken  from  these 
matrices  the  author  has  never  determined,  but  with 
reasonable  care  at  least  a  couple  of  dozen  may  be  made. 
This  is  probably  as  many  as  the  average  worker  will  re- 
quire, but  the  life  of  the  matrices  may  be  prolonged  by 
treating  them  with  an  alum  solution;  in  this  case,  the 
primary  development  of  the  silver  image  must  be  pushed 
a  little  farther  than  usual.  The  alum  bath,  a  ten  per 
cent  solution  of  ordinary  alum  or  five  per  cent  of  chrome 
alum,  should  be  applied  to  the  reliefs  after  they  are 
freed  from  hypo.  They  may  then  be  washed  for  ten 
minutes  and  treated  as  suggested. 

The  advantage  of  this  and  similar  processes  over  the 
pinatype  process  is  that  there  is  nothing  but  the  gelatine 
image  to  stain  up,  so  that  no  dye  can  be  transferred  to 
places  where  it  should  not  be.  Also,  as  all  acid  dyes 
readily  stain  the  gelatine,  and  most  of  them  transfer 
well,  there  is  a  much  wider  choice  of  dyes.  Thus,  one 
may  use  for  the  red  picture,  in  addition  to  those  already 
given,  fuchsin,  erythrosin,  rhodamin  G,  various  sorts  of 
ponceau;  for  the  yellow,  acid  yellow,  naphthol  yellow; 
and  for  the  blue,  diamine  pure  blue  36,  carmine  blue 
and  alizarine  cyanol.  In  fact  one  can  try  out  the  various 
dyes  sold  for  dyeing  household  materials,  and  these  are 
very  cheap. 

If  the  final  dye  impression  is  weak,  or  wanting  in 
details  in  the  high-lights,  the  original  positive  was  under- 
exposed or  underdeveloped,  and  conversely  if  the  high- 
lights show  too  much  color,  particularly  in  portraits,  the 
positive  was  overexposed  or  overdeveloped.  If  the  rela- 
tive coloring  is  good,  but  too  weak  generally,  the  dyed 


88  COLOR  PHOTOGRAPHY 

matrix  was  not  left  long  enough  in  contact  with  the  paper. 
As  with  the  pinatype  process,  corrections  can  be  made 
by  subsequent  transfers  from  one  or  all  of  the  plates. 

It  will  be  found  advisable  to  dye  up  the  matrix  each 
time  before  transfer,  and  it  is  actually  immaterial  how 
long  it  is  left  in  the  dye  solution,  as  the  gelatine  can 
only  take  up  a  certain  amount  of  dye,  and  the  only  point 
to  observe  is  that,  the  more  dye  it  has  absorbed,  the 
more  rapid  the  transfer  to  the  gelatinized  paper. 

THE  ETCHING  PROCESS 

Another  process,  which  is  quite  as  simple  as  that  al- 
ready described,  and  which  is  actually  simpler  if  the 
original  negatives  are  used  as  the  printing  matrices,  is 
the  so-called  etching  process.  In  this  the  gelatine  in  con- 
tact with  the  metallic  silver  of  the  image,  instead  of  being 
insolubilized,  is  chemically  etched  or  dissolved  away. 

This  process  is  founded  on  an  observation  made  origi- 
nally by  Liesegang  in  1897,  and  was  improved  upon  by 
Andresen  in  the  following  year.  The  former  noticed 
that  when  a  negative  was  immersed  in  a  solution  of  am- 
monium persulphate,  the  gelatine  surrounding  the  silver 
image  was  so  softened  that  it  became  soluble  in  hot 
water.  Andresen  improved  the  idea  by  using  hydrogen 
peroxide,  and  this  is  actually  the  etching  agent  in  this 
process,  that  is,  it  gives  up  oxygen  when  reacting  with 
the  silver  and  the  nascent  oxygen  attacks  the  colloid. 
The  etching  fluid  is: 

Hydrogen  peroxide  30.0  ccm 

Cupric  sulphate  20.0  g 

Nitric  acid  5.0  ccm 

Potassium  bromide  0.5  g 

Water  to  1000.0  ccm 


RELIEF  PROCESSES  89 

This  is  used  at  normal  or  room  temperature,  preferably 
18°  C.  (70°  F.)  If  the  temperature  rises,  the  action  is 
apt  to  be  too  violent  in  the  deep  shadows. 

If  one  elects  to  use  the  original  negatives,  it  is  appar- 
ent that  it  obviates  the  making  of  a  set  of  transparen- 
cies and  second  negatives.  There  is  no  real  objection  to 
this  use  of  the  primary  negatives,  except  that  the  gela- 
tine may  become  damaged  in  the  course  of  tune  and  one 
has  then  no  reserve  negatives  to  fall  back  upon,  from 
which  to  make  further  matrices.  It  is  as  well,  therefore, 
to  make  transparencies  from  the  original  negatives  and 
keep  these  in  reserve.  It  may  be  emphasized  here 
(because,  although  we  are  considering  one  special  pro- 
cess, this  recommendation  is  applicable  to  every  case  in 
which  transparencies  are  made  for  the  purpose  of  repro- 
duction of  negatives)  that  they  should  not  be  like  lan- 
tern slides,  that  is,  brilliant  and  hard,  but  rather  of  a 
soft  character,  fully  exposed  without  dense  shadows. 
In  fact  the  best  type  of  reproduction  transparency  is 
that  in  which  there  are  no  patches  of  clear  glass  and  no 
dense  shadows  that  one  cannot  easily  read  print  through. 
One  can,  in  making  the  second  negative  from  such  plates, 
obtain  any  desired  degree  of  contrast  by  the  use  of  con- 
trast plates,  slight  underexposure  or  the  liberal  use  of 
bromide  in  the  developer.  Whereas,  if  the  transparency 
is  wanting  in  detail,  there  is  no  method  of  obtaining  it. 

If  one  elects  not  to  use  the  original  negatives,  one 
must  make  transparencies  from  them  and  duplicate  nega- 
tives from  these.  Obviously  with  all  these  processes,  in 
which  either  negatives  or  positives  are  used  as  print- 
plates,  one  is  not  tied  to  the  original  size  of  the  negatives, 
as  they  may  be  enlarged  or  reduced  in  the  camera,  and 
thus  any  size  of  picture  secured. 


9o  COLOR  PHOTOGRAPHY 

It  is  advisable  to  soak  the  negatives  to  be  used  in  five 
per  cent  chrome  alum  solution  for  about  fifteen  minutes, 
and  then  wash  and  dry;  but  if  films  are  used,  and  these 
are  the  most  satisfactory  because  of  their  pliability,  it  is 
not  necessary  to  use  the  alum  bath. 

The  negatives  should  be  immersed  in  the  etching  solu- 
tion and  allowed  to  soak  for  about  five  minutes,  and  then 
the  dish  gently  rocked,  and  it  will  be  seen  that  the  image 
will  begin  to  gradually  disappear  and  dissolve  off.  If  the 
solution  is  properly  made  up,  the  image  does  not  change 
color  at  all,  but  comes  away  with  the  gelatine  in  its 
original  black  color.  The  solution  becomes  opaque  from 
this  suspended  silver  and  turns  milky,  because  the  bro- 
mide gradually  converts  it  into  silver  bromide.  If,  after 
use,  the  solution  is  allowed  to  stand,  the  bromide  settles 
down  to  the  bottom  of  the  dish  and  the  supernatant 
liquid  can  be  poured  off  and  used  again  if  thought  neces- 
sary; but  as  the  cost  of  the  solution  is  really  very  small, 
this  is  hardly  worth  while. 

The  action  of  the  bath  is  allowed  to  continue  until, 
after  rinsing  the  plate  or  film  with  water,  no  black  image 
is  seen,  which  is  best  observed  against  a  white  surface. 
The  image  will  not  be  quite  invisible,  but  when  there  is 
no  black  silver  visible  the  action  is  complete.  It  is 
always  advisable  to  manipulate  all  three  negatives  at 
once,  or  each  one  with  fresh  solution,  as  this  means  regu- 
larity of  results.  As  the  etching  action  is  due  to  the  evo- 
lution of  oxygen  from  the  peroxide,  and  commercial  per- 
oxide may  be  used,  it  is  clear  that  the  more  the  solution 
is  used  the  longer  it  will  take  to  etch.  If  the  solution  has 
6een  used  and  allowed  to  stand,  and  it  is  thought  worth 
while  to  use  it  again,  it  will  probably  be  unnecessary  to 
add  more  peroxide;  but  more  bromide  should  be  added, 


RELIEF  PROCESSES  91 

because  really  the  quantity  of  bromide  controls  the  ra- 
pidity of  the  solvent  action,  and  if  it  be  entirely  used  up, 
the  silver  may  be  dissolved  without  the  gelatine,  though 
this  is  not  likely  if  the  above  ratios  are  adhered  to. 
Naturally,  also,  increase  in  temperature  increases  the 
rapidity  of  the  action,  but  there  is  no  particular  advan- 
tage in  rapid  action,  and  if  the  rise  in  temperature  is 
about  ten  degrees,  some  of  the  gelatine  not  in  contact 
with  the  silver  may  dissolve;  of  course,  a  rise  of  one  or 
two  degrees  is  of  no  moment. 

As  soon  as  all  the  black  silver  image  has  dissolved,  the 
plate  should  be  washed  for  about  fifteen  minutes  and 
preferably  fixed  in  a  chrome  alum  fixing  bath;  this  is 
not  actually  necessary,  but  as  there  is  always  a  slight 
residue  of  silver  bromide  left  in  the  image,  the  hypo 
removes  it.  Then,  after  washing  out  the  hypo,  which 
takes  but  a  short  tune,  the  plates  should  be  immersed 
in  five  per  cent  solution  of  formaldehyde  for  fifteen 
minutes,  rinsed,  and  dried.  This  drying  hardens  the 
gelatine  so  that  the  image  is  less  liable  to  damage  in  the 
subsequent  operations. 

The  dyes  that  can  be  used  and  the  various  manipula- 
tions are  exactly  as  described  in  the  previous  processes, 
so  that  there  is  no  necessity  to  repeat  the  directions. 
The  print-plates  may  be  repeatedly  used,  staining  up 
afresh  each  time. 

DEVELOPED  RELIEF  PROCESS 

This  is  another  inverse  process,  that  is,  one  in  which  a 
positive  is  used  for  the  print-plate,  which  must  be  ex- 
posed through  the  back.  The  directions  already  given 
for  the  bichromate  relief  process  also  apply  to  this,  and, 


92  COLOR  PHOTOGRAPHY 

as  in  that,  warm  water  is  used  to  dissolve  the  gelatine. 
The  basis  of  the  process  is  the  tanning  action  of  oxidized 
pyrogallol  on  gelatine,  and  this  is  so  great  that  the  lat- 
ter actually  becomes  insoluble  in  warm  water,  as  was 
pointed  out  by  Warnerke  in  1881. 

It  is  a  well-known  fact  that  the  oxidation  of  pyrogal- 
lol, and  all  developing  agents,  is  prevented  by  the  addi- 
tion of  sodium  sulphite  and,  therefore,  by  the  addition 
of  more  or  less  of  this  the  height  of  the  relief  obtained, 
or  the  quantity  of  gelatine  rendered  insoluble,  can  be 
varied.  It  is  possible  to  use  a  plain  solution  of  pyro  with 
soda  or  ammonia,  but  there  is  danger  of  superficial  tan- 
ning, and  as  one  also  wants  freedom  from  fog,  it  is  advis- 
able to  use  some  sulphite  and  some  bromide.  A  suitable 
developer  may  be  made  on  the  following  lines: 

Pyrogallol  5  g 

Sodium  sulphite,  dry  10  to  20  g 
Sodium  carbonate,  dry  25  g 

Potassium  bromide  i  g 

Distilled  water  to  1000  ccm 

The  sulphite  should  be  dissolved  in  100  ccm  of  the  water, 
the  pyro  added,  and  the  solution  at  once  bottled.  The 
carbonate  and  the  bromide  should  be  dissolved  in  900 
ccm  water,  and  when  required  for  use  the  two  solutions 
should  be  mixed.  Obviously,  any  quantity  of  stock 
solution  of  the  carbonate  can  be  made  up;  but  it  is  not 
advisable  to  make  up  any  quantity  of  the  pyrogallol  in 
stock,  as  every  time  the  bottle  is  opened  the  pyro  be- 
comes more  or  less  oxidized,  as  the  amount  of  the  sul- 
phite is  so  small  that  it  is  not  an  efficient  preservative, 
and  consequently  tanning  of  the  gelatine,  where  it  is  not 


RELIEF  PROCESSES  93 

wanted,  might  take  place.  Unless  the  three  transpar- 
encies are  developed  together,  fresh  solution  must  be 
used  for  each  one,  as  otherwise  if  the  developer  be  used 
for  two  or  three  plates  in  succession,  one  meets  with 
precisely  the  same  trouble  again,  because  the  developer 
oxidizes  much  more  rapidly  in  an  open  dish  in  the  pres- 
ence of  the  carbonate  than  in  the  bottle  with  the  plain 
sulphite  solution. 

It  seems  unnecessary  to  repeat  what  has  already  been 
said  when  describing  the  other  processes,  as  to  the  neces- 
sity of  avoiding  underexposure,  but  as  this  developer 
contains  a  fair  proportion  of  bromide  and  this  delays  the 
appearance  of  fine  detail,  it  is  as  well  to  give  a  generous 
exposure  so  as  to  avoid  too  bare  high-lights. 

As  soon  as  development  is  complete,  the  plates  should 
be  at  once  washed  in  water  to  stop  development.  There 
is  no  necessity  to  fix.  They  can  then  be  treated  with 
warm  water  at  about  38°  to  40°  C.  (100°  to  105°  F.),  in 
which  the  gelatine  not  in  contact  with  the  silver  will  dis- 
solve, leaving  a  relief  containing  silver.  It  is  advisable 
to  remove  this,  as  it  renders  the  later  registration  more 
difficult,  and  naturally  any  silver  solvent  may  be  used. 
While  thoroughly  efficient,  the  least  satisfactory  from  a 
practical  point  of  view  is  Howard  Farmer's  hypo  and 
ferricyanide,  as  it  will  not  keep.  The  following  reducer, 
known  as  Belitski's,  is  just  as  efficient,  keeps  well  in  the 
dark,  and  may  be  used  repeatedly: 

Potassium  ferric  oxalate  50  g 

Distilled  water  200  ccm 

Dissolve  and  add: 

Sodium  sulphite,  dry  20  g 

Water  100  ccm 


94  COLOR  PHOTOGRAPHY 

This  at  once  forms  a  blood-red  solution  and  to  it  should 
be  added: 

Oxalic  acid,  dry  crystals  15  g 

Shake  the  solution  until  it  turns  a  fine  green,  without 
any  tinge  of  yellow;  if  this  latter  persists,  and  all  the 
oxalic  acid  has  dissolved,  a  few  more  crystals  of  the  acid 
must  be  added,  and  the  solution  well  shaken;  but  if  the 
solution  is  green  and  there  is  some  undissolved  acid,  the 
mixture  should  be  poured  off  from  the  crystals.  To  this 
solution  should  be  added: 

Hypo  250  g 

Water  to  make  1000  ccm 

When  the  hypo  is  dissolved  the  solution  is  ready  for  use. 
Possibly  some  little  difficulty  may  be  experienced  in 
obtaining  the  potassium  ferric  oxalate,  and  it  should  be 
noted  that  this  is  not  ferric  oxalate;  but  there  is  no  diffi- 
culty in  making  it  by  dissolving  35  g  of  ferric  chloride 
(not  the  anhydrous  salt)  in  50  ccm  water  and  adding  64 
g  of  neutral  potassium  oxalate  dissolved  in  150  ccm 
warm  water.  This  introduces  a  little  potassium  chloride 
into  the  solution,  which  does  no  harm.  After  fixing,  the 
relief  should  be  washed  to  remove  the  hypo  and  dried. 
The  other  steps  in  the  process  are  as  already  outlined  for 
previously  described  methods. 


CHAPTER  IX 
MORDANTING  AND  TONING  PROCESSES 

IN  the  processes  now  to  be  described  the  silver  image 
is  converted  into  some  salt  which  exerts  an  absorptive 
action  on  basic  dyes.  There  is  no  relief  formation  and 
the  dyed  image  is  imbedded  in  the  original  thickness  of 
the  gelatine,  so  that  the  whole  film  has  to  be  transferred 
to  the  final  support.  Consequently  it  will  be  found  that 
films  give  the  least  trouble. 

The  first  process  is  the  diachrome  or  iodide  process, 
which  was  first  described  by  Traube  in  1907.  The  con- 
stituent positives  are  made  in  the  usual  way,  and  after 
fixing  and  washing  are  immersed  in  the  following 
solution  until  the  image  is  seen  to  be  completely 
bleached: 

Iodine  15  g 

Potassium  iodide  50  g 

Glacial  acetic  acid  25  ccm 

Distilled  water  to  1000  ccm 

It  may  be  as  well  to  give  the  best  method  of  making  the 
above  solution.  Add  the  iodide  to  100  ccm  of  water, 
then  stir  in  the  iodine  and  stir  until  completely  dissolved, 
then  add  the  remainder  of  the  water  and  the  acid  to 
make  the  required  volume.  If  the  iodine  and  the  iodide 
are  added  to  the  full  quantity  of  water,  it  takes  a  very 
long  time  for  the  iodine  to  dissolve. 
95 


96  COLOR  PHOTOGRAPHY 

As  a  variant  of  this  bath,  the  image  may  first  be 
bleached  with  cupric  chloride,  by  the  action  of: 

Cupric  sulphate  50  g 

Sodium  chloride  20  g 

Water  1000  ccm 

Wash  after  bleaching,  immerse  in  a  two  per  cent  solu- 
tion of  potassium  iodide  for  fifteen  minutes,  and  wash 
again.  The  first  bath  converts  the  metallic  silver  into 
a  complex  silver-copper  chloride,  which  is  then  converted 
by  the  second  bath  into  the  corresponding  iodide.  Pos- 
sibly an  easier  method,  in  which  copper  iodide  is  at  once 
deposited  on  the  image,  is  by  the  use  of  the  following: 

Cupric  sulphate  50  g 

Water  500  ccm 

Dissolve  and  add: 

Potassium  iodide  33  g 

Water  100  ccm 

A  heavy  precipitate  is  at  once  formed,  and  strong  am- 
monia should  be  added  till  a  perfectly  clear  dark  blue 
solution  is  obtained,  when  the  volume  should  be  brought 
up  to  1000  ccm  by  adding  more  water. 

Whichever  bath  is  used,  the  bleached  image  should  be 
immersed  in  a  five  per  cent  solution  of  sodium  bisulphite 
for  five  minutes.  The  acid  lye  can  be  obtained  com- 
mercially and  can  also  be  made  as  follows: 

Sodium  sulphite,  dry  500  g 

Water  750  ccm 

Stir  well  and  add,  with  constant  stirring,  and  slowly: 
Sulphuric  acid  100  ccm 


MORDANTING  AND  TONING  PROCESSES   97 

This  practically  forms  a  40  per  cent  solution  of  bisul- 
phite, which  is  used  as  a  decolorizing  bath,  as  it  instantly 
attacks  the  free  iodine  that  is  very  tenaciously  held  by 
the  gelatine,  and  decolorizes  it.  The  bleached  positives 
should  be  well  washed  and  can  then  be  dyed  up. 

In  all  these  mordanting  processes  basic  dyes  must  be 
used,  whereas  with  the  relief  processes  acid  dyes  are  em- 
ployed. The  terms  "acid"  and  "basic"  do  not  refer  to 
the  acidity  or  alkalinity  of  the  dye  solutions.  An  acid 
dye  is  one  in  which  the  actual  coloring  matter  is  a  color- 
acid,  and  usually  it  is  combined  with  an  alkaline  base 
such  as  ammonium,  sodium,  potassium  or  calcium.  Such 
dyes  are,  therefore,  salts  of  color-acids.  The  color  ele- 
ment in  a  basic  dye  is  a  color  base  combined  with  an 
acid,  such  as  hydrochloric,  etc. 

The  fact  of  having  to  use  basic  dyes  rather  limits  one's 
choice  and  for  the  red  we  have  fuchsin,  rhodamin  G  and 
3G,  which  are  the  best,  then  Janus  red  B  and  pyronin  G. 
For  the  yellow,  auramin,  vesuvin,  chrysoidin  Y,  thio- 
flavin  and  safranin  Y.  For  the  blue,  Victoria  blue  B, 
night  blue,  methylene  and  thionin  blues. 

The  actual  dye  bath  should  not  be  strong,  certainly 
not  more  than  2.5  :  1000,  and  it  is  advisable  to  add 
about  five  per  cent  of  glacial  acetic  acid.  The  stronger 
the  bath  the  more  rapidly  will  it  act,  but  the  results 
may  be  rather  flat  and  wanting  in  contrast;  whereas 
with  a  weaker  bath,  although  it  takes  a  longer  tune, 
more  brilliant  prints  are  obtained.  As  soon  as  the  pic- 
tures are  sufficiently  stained,  they  should  be  rinsed  to 
free  them  from  excess  dye  on  the  surface.  The  image 
will  now  consist  of  silver,  plus  copper  or  silver  iodide, 
and  the  dye,  and  as  a  rule,  unless  rather  thin  images 
were  obtained  in  the  first  place,  which  is  preferable,  they 


9  8  COLOR  PHOTOGRAPHY 

will  look  too  opaque  and  muddy  because  of  the  silver 
iodide.  To  remove  this  they  have  to  be  fixed,  and  it  is 
here  that  one  is  apt  to  strike  trouble,  as,  on  treatment 
with  an  ordinary  hypo  bath,  the  dye  is  apt  to  diffuse 
into  the  surrounding  gelatine,  or,  as  it  is  technically 
termed,  bleed.  To  prevent  this  the  following  bath  should 
be  used: 

Hypo  150  g 

Sodium  acetate  50  g 

Tannin  5°  g 

Water  to  1000  ccm 

The  prints  should  only  be  left  in  this  until  the  images  are 
sufficiently  transparent,  and  then  immediately  washed. 
The  positives  should  not  be  dense  for  this  process, 
should  be  well  exposed  and  rather  thin,  and  must  be 
quite  free  from  fog.  An  acid  chrome-alum  fixing  bath 
should  be  used,  and  after  washing  they  should  be  im- 
mersed for  fifteen  minutes  in  a  10  per  cent  solution  of 
formaldehyde,  and  dried  without  washing. 

THE  COPPER  MORDANTING  PROCESS 

This  is  somewhat  easier  to  work  than  the  iodide  pro- 
cess, as  there  is  less  chance  of  the  dyes  bleeding;  but  it 
is  more  particularly  suitable  for  the  red  and  yellow  con- 
stituent pictures,  though  it  can  be  used  for  the  blue  as 
well;  it  was  first  suggested  by  Traube  in  1916. 

The  process  is  as  follows:  the  silver  image  is  treated 
with  a  solution  that  converts  it  into  a  mixture  of  silver 
and  cuprous  ferrocyanides,  both  of  which  are  insoluble 
in  water:  the  copper  salt  is  the  mordanting  agent,  the 
silver  ferrocyanide  having  but  little  power  in  this  respect. 


MORDANTING  AND  TONING  PROCESSES  99 

It  is  possible,  therefore,  to  fix  out  the  silver  ferrocyanide, 
leaving  the  copper  salt  and  the  dye.  As  the  former  is 
very  transparent,  it  gives  but  little  trouble  in  the  super- 
position of  the  pictures.  As  stated,  the  only  objection 
to  it  is  that  it  has  a  reddish  tinge  and  this  dulls  the  blues 
and  makes  the  yellows  more  of  an  orange  shade,  though 
this  last  causes  but  little  trouble. 

Copper  toning  processes  for  bromide  prints  have  been 
known  for  a  great  many  years  and  any  of  the  old  for- 
mulas may  be  used,  but  the  following  is  particularly 
suitable: 

Cupric  sulphate  20  g 

Potassium  ferricyanide  15  g 

Potassium  citrate  120  g 
Ammonium  carbonate  10  g 

Water  to  1000  ccm 

In  the  first  place  the  ferricyanide  must  be  in  clear  ruby 
crystals,  without  any  adherent  yellow  powder,  which  is 
the  ferrocyanide.  The  commercial  salt  is  rarely  suffi- 
ciently clean,  and  the  best  thing  to  do  is  to  weigh  out  a 
little  more  than  the  correct  quantity,  say  15.5  g,  place 
this  in  a  small  beaker  and  add  about  100  ccm  distilled 
water,  stir  twice  and  pour  off  the  water.  The  clean  cop- 
per salt  and  the  citrate  should  be  dissolved  in  half  the 
water,  which  may  be  used  warm  with  advantage,  the 
ferricyanide  dissolved  in  250  ccm,  and  the  ammonium 
salt  in  the  remainder.  Warm  water  must  not  be  used 
for  the  latter.  Mix  the  ferricyanide  and  the  ammonium 
solutions  and  add  to  the  copper.  The  positives  should 
be  immersed  in  the  complete  solution  until  there  is  not 
the  slightest  sign  of  a  black  image  to  be  seen  when  ex- 
amined through  the  glass.  This  may  take  from  fifteen 


ioo  COLOR  PHOTOGRAPHY 

to  twenty  minutes.  They  should  then  be  washed  well 
and  may  be  immersed  in  a  20  per  cent  solution  of  hypo 
for  ten  minutes  and  well  washed.  After  toning  they  are 
of  a  somewhat  opaque  reddish  brown  color  when  examined 
by  transmitted  light;  but  after  fixing  they  should  be  a 
clear  transparent  red.  After  being  freed  from  hypo,  they 
should  be  immersed  in  the  dye  solutions,  with  glacial 
acetic  acid,  as  recommended  for  the  iodide  process,  and 
should  be  left  therein  till  sufficiently  stained  up.  If  at 
this  stage  the  image  appears  too  opaque,  or  the  blue  too 
dull,  as  it  may,  the  positive  should  be  immersed  in  a  10 
per  cent  solution  of  sodium  acetate  plus  the  same  quan- 
tity of  tannin  for  ten  minutes,  then  rinsed  and  dipped  into 
a  2  per  cent  solution  of  caustic  soda,  which  dissolves  the 
cuprous  ferrocyanide,  leaving  nothing  but  the  dye  image. 

THE  VANADIUM  MORDANTING  PROCESS 

This  is  actually  an  old  process,  but  its  use  as  a  mor- 
dant was  proposed  by  Namias.  We  have  here  the  same 
basic  reactions  as  in  the  copper  process,  that  is,  the  pre- 
cipitation of  insoluble  vanadium  ferrocyanide  in  situ, 
with  the  formation  of  silver  ferrocyanide;  the  former 
salt  is  yellow,  while  the  silver  ferrocyanide  is  white,  and 
again  it  is  the  other  ferrocyanide  that  acts  as  the  mor- 
dant and  not  the  silver.  The  usual  vanadium  salt  em- 
ployed is  the  chloride,  an  expensive  salt  that  is  so  hard 
to  crystallize  that  it  is  sold  in  syrupy  form.  It  has  the 
great  disadvantage  that  it  forms  silver  chloride,  which 
is  very  opaque.  The  author  has  worked  out  a  method  of 
making  vanadium  oxalate  which  is  comparatively  cheap, 
and  much  more  satisfactory  in  use,  as  it  gives  images  so 
transparent  that  it  is  rarely  necessary  to  fix  them.  The 
following  is  the  method  advised:  place  in  a  porcelain 


MORDANTING  AND  TONING  PROCESSES     101 

evaporating  dish  100  g  ammonium  vanadate  and  460  g 
pure  oxalic  acid,  then  add  gradually  500  ccm  distilled 
water,  and  heat.  The  thick  cream,  which  is  white, 
gradually  becomes  more  fluid  and  turns  first  yellow  and 
then  green  and  the  vanadium  goes  into  solution;  con- 
tinue the  heat  till  the  solution  turns  blue,  then  make  up 
the  bulk  with  distilled  water  to  1477  ccm.  This  will  be  a 
20  per  cent  solution  of  vanadium  oxalate  with  a  slight 
excess  of  acid.  The  sulphate  may  be  made  in  the  same 
way,  substituting  197  ccm  of  pure  sulphuric  acid  for  the 
oxalic;  this  should  form  a  blue  solution,  but  if  not  it 
may  be  heated,  and  the  bulk  in  this  case  also  made  up 
to  the  same  as  before.  Both  solutions  contain  the  same 
ratio  of  vanadium  and  they  will  keep  indefinitely  in  the 
dark,  and  it  is  immaterial  which  is  used.  The  actual  bath 
is: 

Vanadium  oxalate  solution  50  ccm 

Oxalic  acid,  saturated  solution  50  ccm 

Ammonium  alum,  saturated  solution  50  ccm 

Glycerine  50  ccm 

Potassium  ferricyanide,  10  per  cent  solution  10  ccm 
Distilled  water  to  1000  ccm 

The  vanadium,  oxalic  acid  and  alum  should  be  added  to 
half  the  water,  the  glycerine  and  ferricyanide  added  to 
the  remainder,  and  the  two  solutions  mixed.  The  pre- 
vious comments  as  to  the  ferricyanide  apply  equally  in 
this  case. 

The  positives  should  be  immersed  in  the  bath  until  all 
signs  of  a  black  image  have  disappeared  when  examined 
from  the  glass  side,  and  they  can  then  be  washed  and 
dyed  up.  After  treatment  with  the  above  bath,  the 
positives  will  be  found  to  be  of  a  yellowish-orange  color 
and  are  as  a  rule  sufficiently  transparent  without  fixing. 


102  COLOR  PHOTOGRAPHY 

THE  CHEMICAL  TONING  PROCESSES 

These  are  given  rather  with  the  idea  of  making  the 
subject  complete  than  for  their  practical  value,  as  in 
nearly  all  cases  the  images  are  too  opaque  to  be  of  any 
value.  The  iron  toning  process,  however,  which  gives  a 
blue,  has  been  frequently  used  as  the  foundation  image 
for  the  other  colors,  and  the  yellow  mercury  image  may 
be  used  in  the  same  way. 

The  best  way  of  obtaining  the  blue-toned  image,  which 
actually  gives  a  very  satisfactory  foundation  for  the 
other  images,  is  by  a  modification  of  the  bath  given  for 
vanadium,  using  ferric  oxalate  instead.  As  commercial 
ferric  oxalate  is  rarely  suitable  for  the  work,  the  follow- 
ing method  should  be  adopted  for  making  it:  add  520  g 
of  ammonium  iron  alum  to  200  ccm  distilled  water,  and 
heat  until  dissolved.  Then  cool,  add  200  ccm  strong  am- 
monia, and  allow  to  stand  for  fifteen  minutes  with  an 
occasional  stir.  Now  transfer  to  a  tall  1000  ccm  grad- 
uate, and  rinse  the  first  vessel  out  with  repeated  lots  of 
distilled  water  and  add  to  the  graduate  till  full.  Allow 
to  stand  until  the  precipitate  has  settled  somewhat,  then 
syphon  off  the  supernatant  liquid,  fill  up  the  graduate 
again  with  distilled  water,  shake  well,  again  allow  to 
settle,  and  again  syphon  off  the  liquid;  repeat  this 
operation  until  the  water  no  longer  smells  of  ammonia. 
Then  allow  the  graduate  to  stand  until  the  precipitate 
and  the  water  together  measure  not  more  than  850  ccm. 
Add  215  g  pure  oxalic  acid,  stir  well,  and  allow  to  stand 
for  a  short  time.  The  precipitate  will  gradually  dissolve 
and  form  a  bright  green  solution;  when  all  the  red  fer- 
ric hydroxide  has  dissolved,  filter  the  solution  and  add 
distilled  water  to  make  the  bulk  up  to  1000  ccm.  This 


MORDANTING  AND  TONING  PROCESSES     103 

will  be  a  20  per  cent  solution  of  ferric  oxalate  with  an 
excess  of  1.2  per  cent  of  oxalic  acid.  The  addition  of  the 
oxalic  acid  must  be  made  by  artificial  light,  and  the  solu- 
tion must  be  kept  in  the  dark.  The  toning  bath  is  made 
up  exactly  like  the  vanadium  bath,  merely  substituting 
the  iron  for  the  former. 

The  blue  image  given  by  this  bath  is  known  generally 
as  a  cyanotype  or  Prussian  blue  image,  and  it  may  be 
used  as  the  foundation  for  the  red  and  yellow  images,  as 
any  silver  image,  whether  on  paper  or  on  glass,  is  toned 
blue  by  it.  It  is  thus  possible  to  make  the  print  from  the 
minus-blue  negative,  on  bromide  or  development  paper, 
or  on  a  transparency  plate,  and  superimpose  the  other 
images. 

The  yellow-toned  image  is  obtained  by  treating  the 
black  silver  image  with  mercuric-potassium  iodide,  which 
is  made  as  follows: 

Mercuric  chloride  n  g 

Distilled  water  500  ccm 

Heat  until  dissolved,  and  add  the  following  solution: 

Potassium  iodide  27  g 

Distilled  water  500  ccm 

Shake  the  mixture  well  and  filter.  The  print  or  trans- 
parency is  immersed  in  this  solution  for  fifteen  minutes 
and  then  thoroughly  washed.  The  image  turns  brown, 
and  only  after  washing  does  the  yellow  color  appear. 
Another  variation  of  the  above  is  the  following: 

Mercuric  chloride  50  g 

Distilled  water  900  ccm 


104  COLOR  PHOTOGRAPHY 

When  dissolved,  add  slowly  with  constant  stirring: 

Potassium  iodide  2.5  g 

Distilled  water  100     ccm 

In  this  the  image  turns  yellow  at  once. 

There  is  no  satisfactory  method  of  obtaining  a  good 
red  image  by  direct  toning.  There  are  several  methods 
of  obtaining  colored  images  by  the  use  of  lead  salts,  but 
these  are  so  opaque  that  the  resulting  pictures  are  so 
dirty  and  muddy  as  to  be  valueless.  The  blue  toning 
process  described  above  is  satisfactory  for  both  transpar- 
encies and  prints;  but  the  yellow  toning  process  can 
only  be  used  to  make  the  foundation  print,  as  it  is  too 
opaque  for  lantern  slides. 

THE  COMBINATION  OF  PROCESSES 

We  have  dealt  so  far  with  the  various  processes  as 
totally  distinct,  but  it  will  frequently  be  found  that  a 
combination  of  one  or  more  of  these  processes  will  give 
excellent  results.  For  instance,  suppose  the  blue  con- 
stituent picture  is  made  by  blue  toning  of  a  bromide 
print,  then  the  red  and  yellow  images  may  be  made  by 
transfer  by  the  imbibition  method. 

There  is  only  one  disadvantage  in  using  bromide  paper 
for  one  of  the  prints,  and  that  is,  its  unequal  expansion, 
which  may  cause  some  trouble  in  registration.  This  may 
be  overcome  to  a  great  extent  by  soaking  the  paper  in 
water  for  half  an  hour  before  exposure,  which  gives 
it  opportunity  to  fully  expand.  If  a  piece  of  thin  cellu- 
loid be  placed  between  the  negative  and  paper,  the  lat- 
ter may  be  squeegeed  down  to  the  celluloid  and  the  loss 
of  sharpness  is  so  slight  as  to  be  negligible.  Or,  the 


MORDANTING  AND  TONING  PROCESSES     105 

negative  may  be  given  two  coats  of  celluloid  varnish  and 
the  paper  squeegeed  direct  to  it,  and  if  the  paper  be 
stripped  immediately  after  exposure  and  the  negative 
wiped  dry  no  harm  will  ensue.  The  paper  may  be 
treated  before  exposure  with  celluloid  varnish,  the  back 
being  painted  rather  thickly,  which  can  be  easily  done  if 
the  paper  is  placed  in  a  printing  frame  with  a  glass  be- 
hind it  to  hold  it  flat,  the  sensitive  side  being  inside,  of 
course.  Old  celluloid  films,  freed  from  their  gelatine, 
and  dissolved  in  methyl  alcohol  with  acetone  and  a  little 
amyl  acetate,  make  an  excellent  varnish. 

If  the  constituent  pictures  have  been  formed  by  one  of 
the  mordanting  processes,  and  are  thus  carried  by  the 
original  thickness  of  gelatine,  the  best  plan  to  adopt  is  to 
strip  the  films,  and  while  this  may  at  first  sight  seem  a 
ticklish  matter,  it  really  becomes  very  easy  with  a  little 
practice.  The  great  danger  is,  of  course,  expansion  of 
the  gelatine  and  consequent  lack  of  registration;  but,  if 
the  following  directions  are  carefully  followed,  there  is 
little  chance  of  this. 

Place  the  plates  to  be  stripped  on  a  flat  surface,  and, 
with  a  straight  edge  and  a  sharp  penknife,  cut  through 
the  gelatine  film  right  down  to  the  glass,  about  an  eighth 
of  an  inch  from  the  edge  all  round;  this  considerably 
facilitates  later  operations.  The  actual  stripping  solu- 
tion is: 

Glycerine  37-5  ccm 

Water  37-5  ccm 

Hydrofluoric  acid  37-5  ccm 

Denatured  alcohol  to  1000     ccm 

Care  must  be  exercised  in  the  use  of  the  acid,  as  it  read- 
ily attacks  the  finger  nails  and  skin  even  in  this  dilute 


106  COLOR  PHOTOGRAPHY 

strength,  and  when  strong  it  causes  the  most  painful  and 
persistent  burns.  As  the  solution  attacks  glass  and 
enamel,  it  must  be  used  in  papier-mache  or  vulcanite 
dishes;  on  this  property  of  attacking  glass  is  based  its 
stripping  action,  as  it  practically  dissolves  the  surface  of 
the  glass  and  thus  loosens  the  adhesion  of  the  gelatine 
to  the  latter.  It  will  be  found  advantageous  to  make  up 
a  stock  solution  of  the  above  without  the  acid,  and  only 
add  this  just  before  use.  Still  more  desirable  is  the 
abandonment  of  the  acid  altogether  and  its  replacement 
by  an  alkaline  fluoride.  The  commercial  hydrofluoric 
acid  is  a  40  per  cent  solution,  therefore,  in  the  above 
quantity  there  will  be  actually  15  parts  of  acid.  As  we 
can  set  free  the  acid  from  an  alkaline  fluoride  by  the  ac- 
tion of  an  acid,  such  as  sulphuric  or  nitric,  we  may  use 
either  30  g  of  sodium  fluoride  or  44  g  potassium  fluoride 
and  75  ccm  pure  nitric  acid  to  obtain  the  same  result. 
Therefore,  the  procedure  would  be  to  make  a  stock 
solution  of  the  glycerine  and  alcohol  and  add  the  fluoride 
and  acid  just  before  use. 

The  positive  should  be  placed  on  a  level  plate  and  a 
little  of  the  stripping  fluid  poured  on  its  surface  and 
spread  with  a  flat  brush;  this  is  more  convenient  than 
using  a  dish.  In  about  five  minutes  the  film  will  begin 
to  loosen,  and  this  can  be  easily  determined  by  trying  to 
lift  one  of  the  narrow  margins  of  the  film  with  the  pen- 
knife. 

If  this  comes  away  freely  then  one  may  proceed  to 
strip  the  film;  if  not,  a  little  longer  time  should  be  al- 
lowed. In  no  case  must  any  force  be  used  to  lift  the 
film;  it  is  better  to  allow  double  or  treble  the  time  for 
the  solution  to  act  naturally,  as  any  force  will  distort 
it  and  cause  trouble  in  subsequent  registration.  When 


MORDANTING  AND  TONING  PROCESSES     107 

the  film  seems  loose,  gently  lift  the  glass  and  allow  the 
mixture  to  drain  off  slowly  so  as  not  to  give  the  film  a 
chance  to  slip;  then  pour  on  a  little  of  the  stock  solution 
without  the  fluoride,  leave  for  two  or  three  minutes,  and 
then  drain  this  off  in  turn. 

One  may  now  use  either  waxed  paper  or  celluloid  as 
the  transfer  medium.  If  the  latter  is  used,  it  should  be 
thin  and  preferably  rubbed  over  with  a  little  vaseline; 
it  requires  very  little  of  the  latter,  the  merest  dab  just 
rubbed  all  over  the  surface  and  then  well  polished  with 
a  clean  rag  or  two.  Waxed  paper  will  be  found  the 
easier  of  the  two,  but  it  must  be  smooth  and  free  from 
folds,  and  larger  than  the  film.  It  should  be  laid  down 
on  the  surface  of  the  plate  and  very  lightly  squeegeed, 
and  then  the  paper  may  be  lifted  and  it  will  bring  the 
film  with  it  away  from  the  glass. 

An  alternative  method,  which  obviates  the  use  of  the 
fluorides,  is  to  use  an  alkaline  formaldehyde  solution, 
such  as: 

Potassium  carbonate  100  g 

Formaldehyde  100  ccm 

Glycerine  100  ccm 

Denatured  alcohol  300  ccm 

Water  to  1000  ccm 

The  carbonate  should  be  dissolved  in  the  glycerine  and 
water  and  then  the  other  ingredients  added.  The  film 
should  be  cut  round  as  before,  immersed  in  this  solu- 
tion in  a  dish,  and  left  therein  for  from  twenty  to  thirty 
minutes.  The  progress  of  the  stripping  action  is  tested 
by  the  edges,  as  previously  suggested.  When  the 
film  proves  to  be  loosened,  lift  the  plates  from  the  solu- 
tion, drain,  and  immerse  in  a  mixture  of  400  ccm  alcohol 


io8  COLOR  PHOTOGRAPHY 

and  600  ccm  water  for  five  or  ten  minutes,  then  lift  out, 
drain,  and  lightly  squeegee  down  on  the  waxed  paper. 

It  is  advisable  to  treat  all  three  plates  in  this  way 
simultaneously,  so  that  there  may  be  no  delay  in  the 
final  transfer.  For  the  final  support  gelatinized  paper 
is  required,  which  has  already  been  dealt  with.  The 
paper  should  be  larger  than  the  picture.  Having  all 
three  images  on  the  waxed  papers,  the  first  may  be  laid 
down  on  the  dampened  final  support,  lightly  squeegeed, 
and  after  about  half  a  minute  the  wax  paper  may  be 
stripped,  and  then  the  other  images  transferred  in  the 
same  way.  Instead  of  using  the  waxed  papers,  the  final 
support  may  be  squeegeed  direct  to  the  plates,  and  there 
is  even  less  chance  of  non-registration. 

A  cement  is  not  actually  necessary,  but  the  final  result 
is  stronger  if  one  is  used  and  there  is  less  likelihood  of 
the  films  separating.  Either  of  those  already  suggested 
may  be  used,  but  they  must  not  be  too  freely  applied. 
If  the  cement  is  used,  it  is  advisable  so  to  arrange  the 
work  that  each  print  may  be  left  for  about  ten  minutes 
before  the  next  is  applied;  but  the  paper  must  not  be 
allowed  to  dry,  and  should  be  placed  face  up  on  a  pile  of 
wet  blotting  or  filter  papers. 

Another  alternative  is  to  make  two  pictures  on  glass, 
and  the  third  on  thin  celluloid,  printing  through  the  back 
to  obtain  a  reversed  picture  and  then  cement  this  down 
to  the  other  two  transferred  prints,  when  the  celluloid 
acts  as  a  protection  to  the  picture.  For  experienced 
workers  coating  the  constituent  pictures  with  collodion 
will  naturally  suggest  itself  as  a  good  preventive  against 
expansion,  but  for  the  novice,  coating  with  collodion  is 
not  such  an  easy  matter,  and  if  this  be  used  more  tune 
must  be  allowed  for  the  stripping  fluid  to  penetrate.  If 


MORDANTING  AND  TONING  PROCESSES     109 

three  celluloid  films  are  used,  and  this  is  possibly  the 
easiest  plan,  though  there  is  slight  modification  of  the 
colors,  especially  in  the  more  delicate  tints,  because  of 
the  color  of  the  celluloid,  then,  as  we  shall  have  celluloid 
applied  to  gelatine,  a  cement  must  be  used  which  will  act 
on  both,  which  can  be  made  on  the  following  lines: 

Gelatine  2  g 

Pyroxyline  5  g 

Glacial  acetic  acid  50  ccm 

Methyl  alcohol  100  ccm 

Amyl  acetate  20  ccm 

Soak  the  gelatine  in  the  acid  and  melt  by  heat,  dissolve 
the  pyroxyline  in  the  alcohol  and  amyl  acetate  and  add 
to  the  gelatine  solution,  stirring  well,  and,  if  any  gelatine 
is  thrown  out,  heat  a  little  more. 


CHAPTER  X 

THE  THREE-COLOR  GUM-BICHROMATE 
PROCESS 

THIS  is  essentially  a  carbon  process,  and  is  usually 
known  as  the  "bi-gum"  process.  It  is  purposely 
described  separately,  as  it  is  impossible  to  obtain  the 
paper  commercially  and  one  has  to  prepare  it.  After  one 
impression  is  obtained,  it  is  necessary  to  recoat  the  print 
with  the  second  sensitive  mixture,  print,  develop,  and  re- 
coat  for  the  third  print.  It  requires  some  little  experi- 
ence to  carry  this  to  a  successful  conclusion,  and  it  is 
more  time-consuming  than  straight  carbon  printing. 

One  meets  again  in  this  process  the  trouble  of  expan- 
sion of  the  paper,  and  it  is  possibly  more  accentuated. 
The  following  methods  in  addition  to  those  already  given 
may  be  useful.  As  there  is  no  sensitive  surface  to  take 
care  of,  one  has  greater  latitude  in  treatment.  The  most 
radical  treatment  is  to  soak  the  paper  in  water  for 
twenty-four  hours  and  then  squeegee  down  to  a  sheet  of 
glass,  the  edges  of  which  have  been  coated  with  a  10  per 
cent  solution  of  gelatine,  to  which  has  been  added  1.5  per 
cent  of  chrome  alum.  The  edging  should  be  about  half 
an  inch  in  width.  The  wet  paper  will  adhere  to  this 
edging  and  on  drying  contracts  and  becomes  as  tight  as 
a  drumhead.  It  can,  when  dry,  be  painted  with  celluloid 
solution,  such  as: 

Celluloid  12  g 

Methyl  alcohol  750  ccm 

Acetone  or  ether  250  ccm 

Castor  oil  10  ccm 

no 


THREE-COLOR  GUM   PROCESS          in 

Two  or  three  coats  may  be  applied  to  the  dry  paper,  but 
there  should  be  no  glaze  formed;  if  there  is,  more  alcohol 
should  be  added.  When  the  solvents  have  completely 
evaporated,  the  surface  should  be  freely  painted  with  a 
five  per  cent  solution  of  gelatine  containing  one  per  cent 
of  chrome  alum,  and  this  must  be  applied  warm  and 
allowed  to  dry.  Or,  instead  of  the  chrome  alum,  the 
paper,  after  having  been  painted  with  the  plain  gelatine 
solution,  may  be  painted  with  25  per  cent  formaldehyde 
solution  as  soon  as  surface  dry,  and  then  dried.  If  a 
glazed  surface  is  required,  the  commercial  final  transfer 
paper  for  carbon  work  should  be  used,  and  as  this  can  be 
obtained  in  various  surfaces  it  saves  any  preliminary 
preparation. 

The  sensitive  surface  is  prepared  with  gum  arabic  or 
fish  glue  and  gum,  with  which  the  colored  pigments  are 
incorporated,  then  sensitized  with  bichromate,  dried  and 
exposed.  The  development  is  effected  with  cold,  not  hot, 
water,  and  the  print  is  merely  allowed  to  lie  face  down 
on  the  surface  of  the  water,  as  both  the  gum  and  fish 
glue  are  soluble  in  cold  water.  The  print  is  then  im- 
mersed in  alum  solution,  washed,  and  dried. 

The  pigments  used  are  preferably  those  prepared  for 
water-color  painting  and  should  be  obtained  from  an 
artist's  supply  store,  as  these  are  ground  up  specially 
fine  in  water  and  are  free  from  lumps  or  gritty  particles. 
The  preparation  of  the  pigments  is  a  time-consuming  and 
laborious  job;  but  if  anyone  wants  to  do  it,  the  following 
is  the  correct  way  to  set  about  it.  A  glass  muller  and  a 
good  sized  sheet  of  plate  glass  will  be  required.  A  small 
heap  of  the  powdered  pigment  should  be  placed  in  the 
middle  of  the  glass,  a  few  drops  of  water  added,  and  the 
whole  worked  with  the  muller,  water  being  added  gradu- 


U2  COLOR  PHOTOGRAPHY 

ally,  until  a  thick  cream  is  obtained.  Grinding  with  cir- 
cular strokes  is  kept  up  for  about  half  an  hour,  a  few 
drops  of  water  being  occasionally  added  to  prevent  the 
mass  getting  too  dry.  Then  the  pigment  should  be 
scraped  up  with  a  palette  knife  and  put  into  a  wide- 
mouthed  bottle  or  preserving  jar,  and  fresh  pigment 
ground  up  in  this  way  until  the  stock  is  finished.  Care 
must,  of  course,  be  taken  not  to  mix  the  pigments.  Add 
to  the  pastes  in  the  jars  about  ten  tunes  their  volume  of 
water,  stir  or  shake  well,  allow  to  stand  for  about  ten 
minutes  to  allow  the  large  particles  to  settle,  and  then 
pour  off  the  supernatant  fluid  and  allow  to  stand  a  week 
or  ten  days  for  the  fine  pigment  to  settle. 

The  colors  used  should  be  chrome  yellow,  alizarine 
crimson  and  a  mixture  of  Prussian  blue  and  ultramarine 
blue  in  the  ratio  of  4  : 6.  The  gum  solution  is  prepared 
from  good  clean  lump  gum  arabic  (powdered  gum  should 
not  be  used);  200  g  of  the  gum  should  be  placed  in  the 
center  of  a  piece  of  fine  muslin,  the  ends  of  the  latter 
gathered  together  so  as  to  make  a  bag  and  tied  round 
with  a  string;  this  is  then  suspended  in  a  wide-mouthed 
bottle  or  jar,  by  the  aid  of  a  piece  of  wood  across  the 
mouth,  so  that  the  muslin  bag  dips  sufficiently  far  into 
600  ccm  of  distilled  water  to  completely  cover  the  gum. 
This  should  be  placed  in  a  fairly  warm  place  and  left  for 
two  or  three  days  for  the  gum  to  dissolve.  One  can,  of 
course,  merely  add  the  gum  to  warm  water  and  stir  untill 
dissolved,  but  as  the  gum  nearly  always  contains  some 
dirt,  the  method  described  obviates  having  to  filter  or 
strain  the  gum  solution. 

There  are  two  methods  of  preparing  the  paper;  one  in 
which  the  sensitizer  is  mixed  with  the  pigmented  gum, 
and  the  other  in  which  the  latter  is  applied  to  the  paper 


THREE-COLOR  GUM  PROCESS         113 

and  the  bichromate  only  applied  as  one  wants  to  print; 
the  latter  is  preferable,  as  one  can  prepare  a  reasonable 
stock  of  the  pigmented  paper  and  it  will  keep  indefi- 
nitely, whereas  with  the  sensitizer  incorporated  it  will 
only  keep  a  few  days.  If  the  sensitizer  is  to  be  mixed 
with  the  gum,  the  folio  whig  is  a  suitable  mixture: 

Pigment  25  g 

Gum  solution  50  ccm 

Rub  up  well  so  as  to  obtain  a  smooth  mixture,  using 
either  a  mortar  or  a  large  sheet  of  glass  and  a  palette 
knife;  in  the  latter  case  transfer  to  a  tea-cup  or  wide- 
mouthed  jar  and  add  with  constant  stirring: 

Ammonium  bichromate  3  g 

Citric  acid  2  g 

Water  25  ccm 

If  the  sensitizer  is  to  be  applied  afterwards,  this  latter  solu- 
tion may  be  omitted,  and  it  will  then  be  possible  to  prepare 
quite  a  stock  of  the  pigmented  gum,  though  to  prevent 
it  from  moulding  a  few  drops  of  phenol  (carbolic  acid) 
should  be  added.  This  may  also  be  added  to  the  stock 
of  plain  gum  solution  with  advantage,  though  if  the  lat- 
ter goes  sour  and  becomes  more  fluid  it  is  still  fit  for  use. 
There  are  two  methods  of  sensitizing  the  coated  paper, 
either  by  floating  or  by  painting  the  solution  on,  and 
the  latter  is  far  preferable.  If  the  floating  method  be 
adopted,  the  back  of  the  paper,  not  the  coated  surface, 
must  be  floated  on: 

Ammonium  bichromate  30  g 

Citric  acid  15  g 

Water  1000  ccm 


ii4  COLOR  PHOTOGRAPHY 

Float  for  about  five  minutes  and  then  hang  up  to  dry. 
For  painting  on,  half  the  water  in  the  above  formula 
should  be  replaced  with  denatured  or  methyl  alcohol,  and 
the  solution  may  be  freely  painted  on  the  back  of  the 
paper. 

Applying  the  pigmented  gum  to  the  paper  is  somewhat 
of  a  trick,  which  can  be  easily  learned  with  a  little  prac- 
tice, and  that  is  one  reason  why  the  use  of  the  non-sen- 
sitized mixture  is  preferable.  It  is  impossible  to  state 
exactly  how  much  mixture  should  be  used  per  unit  area, 
but  one  soon  learns  from  the  appearance  of  the  paper; 
for  when  finished  it  should  present  an  even  coating  of 
color  and  it  should  not  be  possible  to  see  the  white  sur- 
face through  the  pigment.  Two  brushes  will  be  required, 
a  camel's  hair  mop,  with  which  the  pigment  is  applied 
freely  with  circular  strokes,  and  a  hog's  hair  softener, 
which  should  be  used  first  with  vertical  strokes  and  then 
with  horizontal  ones  until  an  even  coat  is  obtained,  when 
the  paper  may  be  hung  up  to  dry.  The  brushes  must 
not  be  used  too  vigorously  or  a  plentiful  crop  of  minute 
bubbles  will  result,  and  this  particularly  applies  to  the 
use  of  the  second  brush. 

Exposure  is  gauged  with  an  actinometer  as  in  ordinary 
carbon  printing,  and  the  paper  is  rather  more  sensitive 
than  printing-out  paper.  Development,  as  already 
stated,  is  effected  by  floating  the  print  face  down  on 
water,  and  although  this  means  more  time  it  is  the  best; 
twenty  to  thirty  minutes  should  be  allowed,  and  the 
print  may  be  lifted  up  and  examined  from  time  to  time. 
A  spray,  as  from  a  scent  diffuser,  may  be  used,  but  the 
use  of  a  rose  tap  or  pouring  water  direct  on  to  the  sur- 
face from  a  vessel  is  not  advisable,  as  some  of  the  finer 
details  are  sure  to  be  washed  away.  On  the  completion 


THREE-COLOR  GUM    PROCESS         115 

of  development  the  print  should  be  immersed  in  five  per 
cent  alum  solution  for  ten  minutes,  washed  by  repeated 
changes  of  water,  and  dried.  While  wet  the  image  is 
extremely  tender. 

The  second  pigment  is  applied  over  the  first  print  in 
the  manner  described,  and  the  sensitizer  also  used  in 
the  same  way,  but  allowance  must  be  made  for  the  slower 
penetration  of  the  latter,  due  to  the  greater  thickness  on 
account  of  the  presence  of  the  first  print. 

We  now  come  to  the  crux  of  the  whole  process,  the 
registration  of  the  images,  because  it  is  impossible  to  see 
the  outlines  of  the  objects  through  the  pigment  coat. 
The  first  thing  to  do  is  to  see  whether  the  negatives  them- 
selves can  be  registered  by  their  edges  or  corners.  For 
this  purpose  they  should  be  placed  on  a  sheet  of  glass, 
which  should  be  at  least  an  inch  narrower  than  the  nega- 
tives, so  that  both  ends  of  the  latter  protrude  beyond  the 
glass.  The  latter  should  be  supported  on  piles  of  books 
or  in  any  convenient  way,  and  have  a  white  card  under 
it  to  reflect  the  light.  Then  two  diagonally  opposite  cor- 
ners should  be  brought  into  coincidence  and  the  images 
examined.  Care  should  be  taken  to  look  straight  down 
on  them  and  the  use  of  a  magnifying  glass  is  advisable. 
If  two  of  the  negatives  are  thus  found  to  coincide,  the 
third  may  be  compared  with  either  in  the  same  way. 
If  they  all  agree,  further  printing  is  much  facilitated  as 
one  has  merely  to  mark  the  corners  of  the  plates  on  the 
paper,  or  preferably  use  a  printing  frame  larger  than  the 
negatives,  cut  cardboard  corner  pieces,  and  fit  these  into 
the  frame  so  that  the  glasses  will  automatically  drop  into 
register. 

If  the  corners  and  images  do  not  coincide  one  has  a 
much  more  difficult  job.  Six  corner  pieces  of  card  must 


n6  COLOR  PHOTOGRAPHY 

be  cut,  two  of  the  negatives  registered,  the  corner  pieces 
applied  at  opposite  diagonal  corners  and  stout  needles 
driven  through  both,  taking  care  that  the  glasses  do  not 
shift.  The  third  negative  must  now  be  registered  in  the 
same  way,  one  of  those  already  fitted  with  the  corner 
pieces  being  on  top,  and  the  needle  must  be  driven 
through  the  hole  already  made  and  through  the  second 
card.  The  corner  pieces  should  be  numbered  i,  2,  3,  to 
correspond  to  the  negatives,  and  if  they  are  butted  into 
the  corners  of  the  frame  and  registered  by  the  needles, 
the  negatives  will  be  in  register.  It  is  safer,  after  having 
once  made  one  hole,  which  should  not  be  on  the  exten- 
sion of  the  diagonal  of  the  plate,  but  to  one  side,  to  drive 
a  second  needle  through  the  three  cards,  on  the  other 
side  of  the  diagonal,  as  this  prevents  any  possible  shift. 
Naturally  one  may  use  paper  with  any  surface  for  the 
support,  but,  except  for  large  prints,  smooth  papers  are 
preferable,  as  with  really  rough  papers  the  irregularities 
of  the  paper  cause  irregularities  in  the  depth  of  the  pig- 
ment film. 


CHAPTER  XI 
THREE-COLOR  LANTERN  SLIDES 

HAVING  obtained  a  set  of  tri-color  negatives  it  is 
obvious  that  one  can  as  readily  make  lantern  slides 
or  transparencies  as  prints,  and  almost  all  the  processes 
described  for  the  latter  are  applicable  to  slide  making. 

The  easiest  method  is  by  the  use  of  celluloid  film  sen- 
sitized with  bichromate  and  exposed  through  the  back. 
While  roll  film  is  not  ideal,  because  of  the  back  non- 
curling  coating,  it  is  superior  to  the  cut  sheet  film  as  it 
has  only  one-third  the  thickness.  Those  who  like  to 
make  their  own  materials  will  find  it  possible  to  coat 
even  the  thinnest  celluloid  evenly  by  a  little  trick;  the 
difficulty  in  doing  this  is  that  the  celluloid  instantly  curls 
up  on  the  application  of  a  warm  solution.  But  by  the 
use  of  the  following  plan  there  will  be  found  no  difficulty 
from  this.  Clean  some  old  negative  glasses,  of  a  goodly 
size,  and  level  them  carefully.  Prepare  the  following 
mixture: 

Gelatine  S3  g 

Golden  syrup  53  g 

Glycerine  65  ccm 

Chrome  alum  i  g 

Water  to  1000  ccm 

Soak  the  gelatine  in  750  ccm  of  water  with  the  syrup  and 

the  glycerine  for  half  an  hour,  then  melt  by  heat  at 

50°  C.  (120°  F.),  add  the  chrome  alum  dissolved  in  100 

117 


n8  COLOR  PHOTOGRAPHY 

ccm  water,  and  make  up  to  the  quantity  given.  It 
should  be  noted  that  the  syrup  is  cane  sugar  syrup,  not 
corn  syrup,  though  probably  the  latter  will  serve  the  pur- 
pose. Coat  65  ccm  of  the  mixture  on  every  100  square 
inches  of  glass  and  allow  to  set,  and  then  dry;  this  may 
take  twenty-four  hours,  and  one  must  not  be  misled  by 
the  feel  of  the  film,  as  it  actually  never  dries  because  the 
syrup  and  the  glycerine  are  hygroscopic.  The  result  will 
be  a  fairly  thick  tacky  film,  that  will  hold  anything.  If 
the  thinnest  celluloid  be  rolled  down  to  this,  it  will  stick 
for  weeks  unless  pulled  off.  Thus  it  will  remain  perfectly 
flat  while  coated  with  the  various  solutions.  As  soon  as 
these  coatings  have  dried  the  celluloid  may  be  stripped 
by  lifting  two  corners  and  one  edge;  one  of  the  best 
things  to  do  this  is  to  use  a  flat  bone  paper  knife  run 
carefully  along  the  edge  so  as  not  to  damage  the  tacky 
coat;  then  a  straight  steady  pull  will  detach  the  cel- 
luloid. The  tacky  glass  may  be  used  over  and  over 
again;  exactly  how  many  times,  will  depend  on  the  care 
with  which  it  is  handled,  but  at  least  a  couple  of 
dozen  times  is  easily  possible. 

To  prepare  the  gelatine  for  the  sensitive  coating  there 
is  nothing  better  than  the  following: 

Carpenter's  fine  glue  55  g 

Water  500  ccm 

The  glue  is  the  best  and  palest  carpenter's  glue  that  can 
be  obtained,  and  it  should  be  allowed  to  soak  in  the 
water  for  twelve  hours.  The  correct  method  of  working 
is  to  weigh  a  beaker  or  jar  empty,  then  weigh  in  the  glue 
and  measure  the  water;  at  the  end  of  the  time  pour  off 
as  much  water  as  possible  and  weigh  the  jar  again.  Add 
enough  water  to  make  the  weight  660  gm  and  add: 
Gelatine  55  g 


THREE-COLOR  LANTERN  SLIDES       119 

Allow  to  soak  for  half  an  hour,  then  raise  the  tempera- 
ture to  50°  C.  (120°  F.),  and  stir  until  all  is  dissolved, 
then  add: 

Alcohol  40  ccm 

To  this  should  be  added  some  emulsion  of  silver  bromide, 
and  this  is  made  as  follows: 

Gelatine  10  g 

Potassium  bromide  6  g 

Water  100  ccm 

Allow  the  gelatine  to  soak  for  ten  minutes,  melt  by  heat 
at  50°  C.  (120°  F.),  and  add  slowly  with  constant  stirring: 

Silver  nitrate  5  g 

Water  50  ccm 

This  can  be  made  by  artificial  light,  as  the  silver  salt 
merely  plays  the  part  of  an  inert  pigment  and  prevents 
too  high  a  relief;  its  light-sensitiveness  is  not  used. 
Keep  the  emulsion  at  50°  C.  (120°  F.),  for  about  fifteen 
minutes,  and  then  pour  the  emulsion  out  into  a  flat  dish 
to  set,  and  leave  all  night;  if  one  has  a  refrigerator,  the 
dish  should  be  put  in  it  so  as  to  thoroughly  chill  the 
gelatine.  The  next  morning  score  the  emulsion  with  a 
silver  fork  first  lengthwise  and  then  across,  so  as  to  cut 
it  up  into  small  nodules.  Collect  these  in  a  clean  cloth, 
tie  the  ends  of  the  latter  into  a  bag  and  suspend  in 
water;  change  this  six  times  in  the  course  of  half  an 
hour,  giving  the  bag  a  good  squeeze  each  time,  so  as  to 
express  as  much  water  as  possible.  Then  leave  the  bag 
to  drain  for  an  hour,  for  preference  opening  it  and  spread- 
ing the  shreds  out  so  as  to  give  them  a  chance  to  drain 
well.  Melt  at  50°  C.  (120°  F.),  and  add  75  ccm  alcohol. 


120  COLOR  PHOTOGRAPHY 

This  should  be  stirred  into  the  hot  gelatine-glue  mixture, 
and  the  result  should  be  about  1000  ccm  of  a  milky 
emulsion,  which  should  be  made  up  to  that  quantity; 
if  on  the  other  hand  it  measures  a  little  more  it  will  not 
matter. 

There  are  now  two  methods  open,  the  one  to  sensitize 
this,  the  other  to  coat  as  it  is  and  sensitize  as  wanted. 
The  last  plan  is  preferable,  as  one  can  thus  prepare 
enough  celluloid  at  one  sitting  to  last  a  year;  whereas  if 
sensitized  with  bichromate  it  will  not  keep  more  than 
two  or  three  days.  To  sensitize,  30  g  of  ammonium  bi- 
chromate should  be  added  to  the  1000  ccm,  and  it  can  be 
made  to  keep  better  by  the  addition  of  10  g  of  potassium 
citrate.  If  the  gelatine-coated  celluloid  is  prepared,  then 
the  normal  bichromate  sensitizer  should  be  used  as  al- 
ready advised  on  p.  113. 

Printing  is  effected  through  the  back  and,  therefore, 
this  must  be  polished  well.  The  printing  frame  should 
preferably  be  placed  at  the  bottom  of  a  lidless  box,  about 
eighteen  inches  deep,  so  as  to  prevent  the  access  of  side 
light  as  far  as  possible.  The  films  are  very  sensitive,  and 
from  two  to  four  minutes  will  be  about  correct  exposure 
in  bright  diffused  light.  An  actinometer  is  hardly  re- 
quired, as  the  image  can  be  easily  seen  on  the  white 
emulsion.  Printing  should  be  carried  on  until  all  but  the 
details  in  the  highest  lights  are  visible  on  the  back  of  the 
film,  that  is,  on  the  celluloid  side.  Care  must  be  taken  in 
examining  the  progress  of  printing  not  to  expose  the  film 
to  too  bright  a  light,  or  more  or  less  general  insolubility 
will  be  caused.  After  exposure,  the  films  are  developed 
in  warm  water  at  a  temperature  not  exceeding  45°  C. 
(113°  F.),  and  the  progress  of  development  is  easily  seen, 
as  the  silver  bromide  acts  as  a  pigment.  As  soon  as  the 


THREE-COLOR  LANTERN  SLIDES       121 

picture  is  developed,  immerse  in  cold  water.  One  now 
has  a  carbon  or  gelatine  picture  with  the  silver  bromide 
as  pigment,  and  as  this  is  now  valueless,  having  done  its 
work,  it  must  be  removed,  either  by  using  a  hypo  bath, 
or  what  is  preferable,  hypo  and  ferricyanide  or  the  re- 
ducer given  on  p.  93.  The  reason  for  advising  the  use 
of  these  is  that  the  silver  salt  may  be  so  far  reduced  by 
the  exposure  as  to  be  actually  darkened  and  as  this 
means  metallic  silver  it  darkens  the  colors.  A  good  wash 
should  follow,  and  the  reliefs  may  be  dyed  up,  or  dried 
and  subsequently  dyed. 

Any  of  the  relief  processes  already  described  for  prints 
may  be  used  here,  and  for  this  work  the  best  film  to  use 
is  motion  picture  positive  film,  which  can  be  usually 
obtained  to  order.  This  is  on  celluloid  only  0.005  mch 
thick  and  has  no  back  coating;  the  emulsion  is  excellent 
for  positive  making,  though  rather  faster  than  the  usual 
run  of  transparency  plates. 

As  regards  the  dyes  for  staining  up,  one  has  a  fairly 
wide  range,  as  acid  dyes  are  the  best.  The  following 
baths  were  suggested  by  Lumiere,  and  their  only  dis- 
advantage is  that  the  dyeing  is  very  slow.  On  the  other 
hand,  it  must  be  recognized  that  the  most  brilliant  re- 
sults are  obtained  with  slow  dyeing,  that  is,  in  weak 
solutions;  strong  solutions  and  rapid  dyeing  always  give 
flat  pictures. 

For  the  red: 

Erythrosin  1.5  g 

Water  1000  ccm 

Time  of  dyeing  from  one  to  five  hours.  Rinse  with  water 
and  immerse  for  five  minutes  in  five  per  cent  solution  of 
cupric  sulphate. 


122  COLOR  PHOTOGRAPHY 

For  the  yellow: 

Chrysophenin  (aurophenin)  2  g 

Water  1000  ccm 

Dissolve  by  heat  and  add: 

Alcohol  200  ccm 

The  great  disadvantage  of  this  dye  is  that  it  must  be 
used  in  the  form  of  the  ammonium  salt,  and  forms  in- 
soluble muddy  brownish  colors  with  calcium  salts;  there- 
fore the  relief  must  be  immersed  in  a  i  per  cent 
solution  of  hydrochloric  acid  for  five  minutes  and  then 
washed  in  distilled  water,  before  staining;  it  is  as  well, 
therefore,  not  to  use  this. 
For  the  blue: 

Pure  diamine  blue  FF  2  g 

Fish  glue  12  ccm 

Water  1000  ccm 

Dyeing  takes  from  two  to  ten  hours.  The  glue  causes 
a  slower  and  more  even  dyeing.  This  picture  should  be 
immersed  in  the  copper  bath  after  rinsing,  but  this  treat- 
ment is  not  necessary  for  the  yellow. 

Von  Hiibl  recommended  the  following,  which  do  not 
take  so  long  as  the  previous  baths.    For  the  red: 
Erythrosin  0.25  g 

Alcohol  ico  ccm 

Water  to  1000  ccm 

For  the  yellow: 

Naphthol  yellow  S  0.5  g 

Alcohol  100  ccm 

Glacial  acetic  acid  5  ccm 

Chrome  alum,  saturated  solution  50  ccm 

Water  to  1000  ccm 


THREE-COLOR  LANTERN  SLIDES       123 
For  the  blue: 

Bluish  fast  green  o.i  g 

Alcohol  100  ccm 

Glacial  acetic  acid  5  ccm 

Water  to  1000  ccm 

Other  dyes  as  suggested  for  prints  may  be  used;  for 
the  red,  rhodamine  B,  or  better  still  xylene  red  B,  are 
good,  for  the  blue,  patent  blue  V,  and  for  the  yellow, 
mikado  yellow. 

One  of  the  best  methods  of  working  is  to  use  acid  and 
basic  dyes,  as  this  gives  one  a  much  greater  range  and 
power  over  the  colors  and  it  is  extraordinary  what  deep 
colors  can  be  obtained.  This  method  of  working  is  based 
on  the  fact  that  the  acid  and  basic  dyes  mutually  pre- 
cipitate one  another,  so  that  it  is  possible  to  faintly  stain 
up  with  an  acid  dye  and  then  by  treatment  with  a  basic 
dye  to  obtain  a  very  deep  result,  or  the  order  of  the  dyes 
may  be  reversed.  This  method  was  originally  suggested 
by  J.  H.  Powrie,  and  elaborated  by  A.  E.  Bawtree,  whose 
choice  of  dyes  is  followed.  For  blue,  soluble  blue  5  per 
cent,  oxalic  acid  5  per  cent;  for  peacock  blue,  which 
gives  the  best  colors,  soluble  blue  5  per  cent,  naphthol 
green  i  per  cent,  malachite  green  5  per  cent.  For  yellow, 
aurantia  2  per  cent,  auramin  0.3  per  cent.  For  red,  rose 
Bengal  10  per  cent,  auramin  o.i  per  cent.  The  method 
of  using  these  is  to  immerse  the  picture  in  the  first 
named  dye  for  a  short  time,  then  wash  and  immerse  in 
the  second;  for  instance  for  yellow  immerse  in  the  auran- 
tia first,  then  in  the  auramin.  This  alternation  of  the 
baths  can  be  repeated,  with  intermediate  slight  washings, 
till  sufficient  depth  is  obtained;  this  in  fact  may  be 
likened  to  a  species  of  dye  intensification. 


124  COLOR  PHOTOGRAPHY 

The  pinatype  process  gives  very  brilliant  transpar- 
encies, but  it  is  a  little  trouble.  Glass  should  be  coated 
with  5  per  cent  solution  of  hard  gelatine  containing  2  per 
cent  of  ammonium  bichromate,  and  30  ccm  should  be 
allowed  for  every  100  square  inches.  Weak  daylight  or 
artificial  light  may  be  used,  but  the  plates  must  be  dried 
in  the  dark.  They  will  keep  for  about  fourteen  days, 
but  it  is  better  to  coat  the  glass  with  plain  gelatine  solu- 
tion and  sensitize  as  wanted.  Transparencies  must  be 
used  to  print  from,  and  it  is  advisable  to  print  from  the 
minus  red  one  first,  that  is,  from  the  transparency  taken 
through  the  green  filter.  It  is  then  washed  with  water 
until  free  from  bichromate,  or  to  save  time  it  may  be 
immersed  in  a  2  per  cent  solution  of  sodium  bisulphite, 
and  washed  and  dyed  up.  It  must  now  be  dried,  placed 
on  a  leveled  stand,  coated  again  with  the  bichromated 
gelatine  and  dried.  The  minus  blue  transparency,  taken 
through  the  red  filter,  should  be  placed  over  the  film  and 
registration  secured  by  the  aid  of  a  magnifier;  the  two 
plates  are  kept  from  shifting  by  two  strong  metal  clips,  or 
a  printing  frame  can  be  used.  The  exposure  is  about 
twice  as  long  as  for  the  red  impression,  because  some  of 
the  bichromate  penetrates  into  the  red  image,  so  that 
the  sensitiveness  is  reduced,  and  an  increase  of  the 
bichromate  is  not  advisable.  After  printing,  the  plate  is 
washed  or  treated  with  the  bisulphite,  and  dyed  up. 
The  yellow  impression  is  obtained  in  the  same  way; 
but  it  is  easier  to  make  the  yellow  picture  on  another 
glass  and  reverse  it,  so  that  it  can  be  used  as  the  cover 
glass  for  the  red-plus-blue  image. 

In  all  these  processes,  the  blue  constituent  may  be 
obtained  by  the  aid  of  a  silver  image,  and  this  toned  with 
the  cvanotype  mixture  as  already  described.  A  combina- 


THREE-COLOR  LANTERN  SLIDES       125 

tion  of  processes  can  also  be  used,  excellent  results  being 
obtained  by  making  a  blue-toned  picture  and  transfer- 
ring the  red  and  yellow  to  it  by  the  imbibition  method. 
Enough  has  probably  been  said  to  lead  the  beginner  in 
the  right  road  to  making  successful  lantern  slides,  for 
after  all  a  slide  or  transparency  is  nothing  more  than  a 
print  with  glass  as  a  support  instead  of  paper.  Attention 
to  details  and  extreme  cleanliness  in  working  are  essen- 
tial, and  above  all  things  absolute  freedom  from  dust,  as 
this  shows  up  most  distinctly  when  projected  on  a  large 
scale  on  the  screen. 

THE  PHOTOCHROMOSCOPE 

Instead  of  using  superposed  subtractive  pictures  it 
is  possible  to  make  use  of  the  additive  superposition 
of  the  pictures,  by  means  of  an  instrument  called  the 
photochromoscope  or  chromoscope. 

Then,  instead  of  each  individual  constituent  positive 
being  colored  in  the  subtractive  or  complementary  color, 
ordinary  black  and  white  transparencies  are  used,  which 
are  illuminated  by  the  three  fundamental  colors  and  are 
optically  superposed,  giving  the  impression  of  a  complete 
colored  picture.  The  results  obtained  by  this  method  are 
extremely  pleasing,  especially  when  seen  stereoscopically, 
but,  as  in  the  stereoscope,  only  one  person  can  examine 
the  results  at  one  time. 

The  following  instructions  should  enable  anyone  to 
make  one  of  these  instruments;  these  have  been  taken 
from  Konig's  work,  as  they  are  the  only  working  instruc- 
tions that  have  been  published.  The  instrument  is  shown 
in  section  and  plan  in  the  accompanying  diagrams.  Fig. 
15  shows  a  section  of  the  chromoscope;  the  box  is  made 
with  steps  with  apertures  at  L,  L',  L"  for  the  light 


126 


COLOR  PHOTOGRAPHY 


filters  and  transparencies.  M  and  M '  are  two  transparent 
mirrors  at  an  angle  of  45  degrees  to  the  bottom  of  the 
box.  R  is  a  mirror  or  white  card  or  preferably  a  sheet  of 
opal  glass,  which  is  hinged  so  as  to  allow  of  adjustment 
to  obtain  the  best  illumination  of  the  aperture  L".  The 
transparencies  are  placed  on  top  of  the  filters.  The  eye 


FIG.  15 

sees  through  O  the  transparency  placed  at  L"  through 
the  mirrors  M  and  M' .  The  picture  at  L'  is  reflected  by 
the  mirror  M'  and  passes  through  M  to  the  eye.  The 
picture  at  L  is  reflected  by  the  mirror  M  to  the  eye  at  O. 
The  last  two  pictures  are  thus  seen  in  an  inverted  and 
upright  position  at  L"  and  combine  with  the  picture 
which  actually  is  at  this  plane.  The  measurements  are 
so  adjusted  that  the  three  pictures  fuse  into  one. 


THREE-COLOR  LANTERN  SLIDES       127 

As  the  image  of  a  mirrored  object  appears  to  be  as  far 
behind  a  mirror  as  the  object  itself  is  in  front  of  the  mir- 
ror, LM  must  be  equal  to  ML",  and  L'M'  equal  to  M'L". 
Therefore,  LM-L'M'  must  equal  ML" -M'L",  or  the 
distance  of  the  mirrors  M  and  M'  from  one  another 
must  be  equal  to  the  distance  of  L  from  L'. 

The  wood  may  be  any  well-dried  kind,  about  i  cm 
thick,  which  will  not  warp.  For  px  12  cm  pictures,  or 
practically,  with  suitable-sized  apertures,  for  3^  x  4^  or 
4x5  plates,  the  outside  measurements  should  be  about 
as  follows: 

ni  in. 

6£  in. 

lof  in. 

5l  in- 

6^  in. 
5rt>in. 

The  horizontal  surfaces  AGKF  and  HJEM  have  an  aper- 
ture of  about  10  x  13  cm  exactly  in  the  middle;  the  ver- 
tical surface  CDEJ  also  has  a  similar  size  aperture,  the 
upper  edge  of  which  is  exactly  as  far  from  JE  as  the  near- 
est edge  of  the  aperture  HJEM  is  from  JE.  One  side 
wall  carries  a  flap  which  is  provided  with  hinges  and 
turn-buckle,  which  is  just  large  enough  for  the  reflector 
R  with  the  base  that  carries  it  to  be  stored  away  inside 
the  box. 

On  a  board  of  exactly  the  size  of  the  inner  bottom  sur- 
face of  the  box  the  two  mirrors  M  and  M'  (Fig.  15)  are 
fastened.  These  mirrors  should  measure  about  135  x  135 
mm,  and  are  placed  with  their  lower  edges  screwed  on 
two  metal  angle  plates  which  should  be  screwed  to  the 


AB 

285  mm 

CD,AF 

165  mm 

BC 

265  mm 

AG 

135  mm 

EG 

125  mm 

CJ 

160  mm 

HJ 

130  mm 

128 


COLOR  PHOTOGRAPHY 


board.  The  shorter  side  of  these  plates  should  slope 
about  5  mm  above  the  board.  The  longer  side  should 
have  a  slit  about  25  mm  long,  through  which  passes  the 
binding-screw.  This  slit  enables  one  to  shift  the  position 
of  the  mirrors  slightly.  The  mirrors  are  supported  be- 
hind by  two  screws  C  and  C',  by  means  of  which  the  an- 
gle of  the  mirrors  can  be  slightly  altered.  These  screws 


B    e±l 


FIG.  16 

should  be  perpendicular  to  the  surface  of  the  mirrors, 
that  is,  at  an  angle  of  45  degrees  to  the  bottom  of  the 
box.  In  order  to  support  the  mirrors  they  may  have 
on  their  upper  edges  a  narrow  metal  strip,  to  which  may 
be  soldered  a  hard  brass  or  steel  spring,  which  may 
be  hooked  to  the  baseboard,  or  to  little  blocks  of  wood 
projecting  from  the  sides  of  the  box. 

The  distance  of  the  two  mirrors  from  one  another  is 
the  same  as  GH  (Fig.  16),  that  is,  125  mm.     The  rear 


THREE-COLOR    LANTERN    SLIDES       129 

mirror  should  almost  touch  the  back  wall  CDEJ  at  the 
top.  The  transparency,  placed  at  L"  (Fig.  15),  should  be 
illuminated  by  the  mirror  or  reflector  R,  which  should  be 
adjustable,  so  as  to  enable  the  best  illumination  to  be 
obtained.  The  whole  apparatus  should  be  fastened  to  a 
stout  baseboard,  so  that  it  may  be  directed  to  the  sky 
or  any  illuminant  that  is  used. 

An  aperture  should  be  cut  in  the  front  wall  ABF,  like 
the  lens-board  of  a  camera  front,  and  the  piece  again 
fitted  in  with  screws  and  turn-buckles.  In  this  cut-out 
piece  should  be  fastened  an  ordinary  bi-convex  or  read- 
ing glass  of  from  35  to  40  cm  focus,  so  that  its  center  or 
optical  axis  should  be  exactly  level  with  the  middle  of  the 
aperture  CDEJ.  This  lens  need  not  be  achromatic;  one 
of  the  ordinary  reading  glasses  is  quite  satisfactory.  As 
large  a  lens  as  possible  should  be  chosen,  so  that  both 
eyes  may  be  used;  and  the  lens  should  be  blocked  out 
with  black  paper  or  a  metal  frame  so  that  only  a  horizon- 
tal slit  remains  for  the  eyes  to  look  through.  The  inside 
of  the  apparatus  should  be  painted  dead  black,  so  that 
no  white  light  is  reflected  to  the  eye.  An  ordinary  shel- 
lac varnish,  thinned  with  alcohol,  and  mixed  with  lamp- 
black, so  as  to  give  a  dead  surface,  may  be  used,  or  the 
wood  may  be  chemically  stained. 

As  pointed  out  on  page  24  we  must,  as  this  is  an  additive 
process,  use  the  fundamental  colors  for  the  filters,  which 
are  placed  in  the  three  apertures  L,  L',  L",  and  which 
illuminate  the  three  transparencies.  The  latter  must  be 
placed  on  filters  of  the  same  color  as  was  used  to  make 
the  negatives,  that  is,  the  transparency  from  the  negative 
taken  through  the  red  filter  must  be  illuminated  by  red 
light,  the  green  transparency  by  green  and  the  blue  by 
blue-violet  light.  The  filters  for  this  purpose  may  be 


I3o  COLOR  PHOTOGRAPHY 

those  suggested  on  pages  171, 173  for  screen-plate  printing, 
or  may  be  made  from  the  following  stock  solutions  of 
dyes.  As  these  filters  are  merely  used  as  light  absorbers, 
or  screens,  and  are  not  required  to  give  accurate  images, 
there  is  no  need  to  be  so  careful  in  their  preparation 
as  with  taking  filters,  that  is  to  say,  they  need  not  be 
cemented  nor  need  the  glass  be  optically  so  perfect  as  in 
the  latter  case;  old  negative  glasses,  free  from  bubbles 
and  scratches,  may  be  used  with  satisfactory  results.  But 
it  is  important  that  the  coatings  should  be  as  even  as 
possible.  Two  colored  screens  should  be  placed  film  to 
film  for  each  color,  as  it  is  thus  possible  to  obtain  more 
even  results. 

It  is  advisable  to  make  up  stock  solutions  of  the  dyes 
and  add  these  to  plain  gelatine  solution.  The  stock  solu- 
tion for  the  blue  filter  is  made  from: 

Crystal  violet  3  g 

Methylene  blue  i  g 

Glacial  acetic  acid  5  to  6  drops 

Warm  water  100  ccm 

A  6  per  cent  solution  of  plain  gelatine  will  also  be  re- 
quired. The  actual  dyed  gelatine  should  be: 

Gelatine  solution  747  ccm 

Dye  solution  23  ccm 

This  is  sufficient  for  i  square  meter  of  filter  surface. 

For  the  green  filter  the  following  stock  solution  should 
be  prepared: 

Tartrazin  6  g 

Patent  blue  i  g 

Naphthol  green  2  g 

Warm  water  180  ccm 


THREE-COLOR   LANTERN    SLIDES      131 

The  green  filter  is  the  one  that  gives  the  most  trouble 
and  requires  the  most  adjustment  so  as  to  obtain  white 
light,  for  the  three  filters  must  give  white  light  at  the  eye- 
hole 0.  It  is  as  well,  therefore,  to  make  about  five  fil- 
ters of  different  depths  of  coloring,  which  can  be  done  by 
adding  varying  quantities  of  the  dye  solution  to  the  plain 
gelatine: 

Gelatine  solution  690  ccm 

Dye  solution  8  to  16  ccm 

It  is  as  well  to  start  with  8  ccm  of  the  dye  solution,  and 
then  make  other  mixtures  with  10,  12,  14  and  16  ccm  of 
dye  solution,  so  that  five  different  depths  of  filters  will 
be  obtained.  The  above  quantity  is  sufficient  for  i 
square  meter  of  filter  surface. 

The  red  filter  should  be  made  with  the  following  stock 
solution: 

Tartrazin  4    g 

Rose  Bengal  3.5  g 

Water  150    ccm 

The  actual  dyed  gelatine  will  be: 

Gelatine  solution  432  ccm 

Dye  solution  38  ccm 

This  is  sufficient  for  i  square  meter  of  surface. 

As  the  mirrors  M  and  M'  must  not  only  reflect  the 
pictures  at  L  and  L',  but  also  transmit  that  at  L", 
ordinary  mirrors  are  not  suitable.  Half  silvered  or 
platinized  mirrors  may  be  uctd,  but  these  are  costly  and 
easily  tarnish,  so  that  plate  glass  should  be  used,  and  as 
they  should  not  reflect  the  pictures  from  the  back  sur- 


I3 2  COLOR  PHOTOGRAPHY 

/ 

faces  they  ought  to  be  colored.  The  easiest  way  to 
make  these  is  to  coat  them  with  dye  solutions,  and 
they  should  be  cemented  to  plain  glasses  with  Canada 
balsam. 

The  dyed  gelatine  for  the  green  mirror  should  be  made 
from  the  following  stock  solution: 

Tartrazin  0.5  g 

Naphthol  green  0.8  g 
Patent  blue  1.2  g 

Water  250  ccm 

To  every  100  ccm  of  the  plain  gelatine  solution  should 
be  added  8  ccm  of  the  dye  solution,  and  the  mixture 
filtered.  For  a  mirror  135  x  135  mm,  13  ccm  of  the  dyed 
gelatine  should  be  used. 

For  the  blue  mirror  use  the  following: 

Patent  blue  i  g 

Warm  water  100  ccm 

To  every  100  ccm  of  gelatine  solution  allow  4  ccm  of 
the  dye  solution  and  coat  the  same  quantity  as  above, 
namely  13  ccm,  on  the  same  size  mirror. 

These  colored  mirrors  should  now  be  fastened  in  the 
box  at  an  angle  of  45  degrees  with  the  base.  The  blue 
mirror  should  be  placed  under  the  red  filter,  and  the 
green  mirror  under  the  blue  filter. 

The  instrument  should  be  inclined  towards  the  sky  and 
the  inclination  of  the  mirrors  altered  until  the  images  of 
the  filter  apertures  are  seen  as  far  as  possible  in  coinci- 
dence. It  is  advisable  to  cover  one  of  the  apertures  and 
adjust  one  mirror  first,  and  then,  having  obtained  satis- 
factory agreement  (narrow  colored  fringes  at  the  margins 
can  be  ignored),  cover  up  the  aperture  just  brought 


THREE-COLOR    LANTERN    SLIDES      133 

into  coincidence  and  use  the  third  aperture  in  the  same 
way. 

If  the  filters  are  correct,  the  field  of  view  should  be 
whitish  and  very  bright;  but  care  must  be  taken  to  use 
the  reflector,  as  if  this  is  not  done  one  or  other  of  the 
colors  will  predominate.  If  the  field  is  too  red  the  green 
filter  is  too  dark;  with  a  greenish  field  the  green  filter  is 
too  bright.  And  it  is  here  that  the  use  of  the  extra 
niters  comes  into  play,  as  one  can  substitute  one  for  the 
other  till  a  good  white  is  obtained.  If  the  field  is  yel- 
lowish, the  blue  filter  is  too  dark;  if  it  is  blue  the  red 
filter  is  too  dark  or  the  blue  filter  is  too  bright.  As  a 
rule  if  the  filters  are  prepared  as  advised  above  it  is 
only  the  green  filter  that  will  require  adjustment.  An 
absolute  white  is  extremely  difficult  to  obtain,  but  a 
great  preponderance  of  one  or  the  other  color  can  be 
avoided. 

As  soon  as  the  correct  niters  have  been  found  they 
should  be  permanently  fixed  in  the  apertures.  To  hold 
the  transparency  at  L",  two  wooden  or  metal  grooves 
should  be  provided.  At  L  and  L'  spring  metal  clips  can 
be  used. 

The  green  filter  should  be  placed  at  L",  the  red  may 
be  either  at  L  or  L',  and  the  transparency  from  the 
green-filter  negative  should  be  placed  here.  The  red- 
filter  transparency  should  be  placed  on  the  red  filter  and 
the  blue  on  the  blue  filter.  The  latter  should  be  tem- 
porarily covered  with  an  opaque  card,  and  the  red 
transparency  shifted  till  the  outlines  of  the  images  co- 
incide, and  then  the  card  removed  from  the  blue  picture 
and  this  adjusted  in  register. 

If  the  measurements  of  the  instrument  are  not  ex- 
actly correct,  the  three  images  may  coincide  but  may  not 


i34  COLOR  PHOTOGRAPHY 

lie  in  the  same  plane;  for  instance,  the  red  image  may  be 
in  front  or  behind  the  green. 

If  the  red  image  is  in  front  of  the  green  transparency, 
the  distance  LM  is  too  small;  if  it  lies  behind,  LM  is  too 
great.  This  may  be  remedied  by  shifting  the  mirror  M 
backwards,  or  by  altering  the  distance  LM  or  GH.  It 
is  as  well  to  bear  this  in  mind  when  making  the  appara- 
tus and  arrange  so  that  the  heights  GH  and  CJ  may  be 
slightly  altered  by  inserting  a  wooden  frame  or  planing 
off  a  little.  This  regulation  requires  to  be  done  only 
once,  while  the  focusing  of  the  images  must  be  done  each 
time.  To  avoid  adjusting  it  each  time,  the  following  plan 
may  be  adopted:  the  red  and  blue  transparencies  should 
be  provided  with  narrow  card  margins,  which  should  be 
stuck  on.  On  the  edges  GK  and  JE  should  be  fastened 
a  T-square  of  wood  or  metal,  only  a  few  millimeters  long, 
against  which  the  picture  edge  should  be  laid.  It  will 
now  be  easy  by  careful  and  gradual  paring  away  of  the 
card  to  so  arrange  that  the  transparencies  at  once  co- 
incide, and  they  will  then  only  have  to  be  pressed  up 
against  the  T-square  to  fall  in  register. 

Frequently  great  improvement  may  be  effected  by 
placing  over  the  green  filter  other  green  glasses  of  faint 
tint,  which  can  be  prepared  by  coating  glasses  with  vary- 
ing amounts  of  the  green-dyed  gelatine.  These  compen- 
sate for  the  varying  composition  of  daylight.  It  is  not 
possible  to  use  artificial  lights  with  this  instrument,  un- 
less the  composition  of  the  light  is  brought  to  approxi- 
mately the  same  as  daylight.  The  instructions  given  for 
the  preparation  of  the  viewing  filters  for  screen-plates  on 
page  165  may  be  followed. 

With  such  an  instrument  one  may  perform  many  in- 
teresting experiments,  which,  although  not  color  photog- 


THREE-COLOR   LANTERN   SLIDES      135 

raphy,  are  well  worth  trying.  For  instance,  by  placing 
the  transparencies  in  the  wrong  apertures  all  sorts  of 
colored  results  may  be  obtained.  Negatives  may  be  used 
and  then  images  in  the  complementary  colors  will  be 
seen.  And  obviously  by  covering  up  any  aperture  the 
complementary  color  is  at  once  seen  from  the  admixture 
of  the  other  two.  By  using  cut  out  patterns,  too,  some 
wonderful  color  effects  can  be  obtained. 


CHAPTER  XII 
SCREEN-PLATES 

THE  fundamental  idea  of  the  screen-plate  was  con- 
ceived by  Ducos  du  Hauron  in  1867.  It  belongs 
to  the  additive  processes,  and  the  principle  is  similar  to 
a  particular  school  of  painting,  in  which  small  areas  of 
pure  pigments  are  juxtaposed  to  produce  a  given  color 
effect,  when  seen  at  a  certain  distance.  Thus,  if  we  wash 
paper  with  rose  Bengal,  which  is  a  bright  crimson  ani- 
line dye,  and  then  apply  a  wash  of  malachite  green, 
the  result  will  be  a  dirty  brown;  but  if  instead  of  super- 
imposing the  colors  we  use  them  in  small  areas  side  by 
side,  the  result  when  examined  at  a  little  distance  is  a 
yellow.  Exactly  in  the  same  way  blue- violet  and  green 
on  top  of  one  another  would  give  a  dirty  olive,  but  jux- 
taposed in  minute  dots  we  obtain  a  pure  blue;  and  the 
violet  and  red  in  the  dotted  form  will  give  a  pure  crimson. 
The  idea  of  Ducos  du  Hauron  lay  dormant  for  many 
years,  until  in  1892  J.  Joly,  of  Dublin,  and  J.  W.  Mc- 
Donough,  of  Chicago,  conceived  methods  of  putting  it 
into  practice,  and  for  this  purpose  ruled  glasses  with 
fine  red,  green  and  blue  lines,  about  200  to  300  to  the 
inch.  Such  a  screen  was  placed  in  contact  with  a  pan- 
chromatic plate,  exposed,  and  developed.  From  the  line 
negative  thus  obtained  ordinary  silver  transparencies 
were  made  and  bound  up  in  register  with  similarly  ruled 
screens,  and  the  results  were  excellent  in  color.  Commer- 
cially, the  process  was  a  failure,  because  of  the  cost  of 
136 


SCREEN-PLATES  137 

ruling  the  plates,  and  the  want  of  a  really  satisfactory 
panchromatic  plate.  In  1907  the  Lumiere  Co.,  of  Lyons, 
France,  introduced  the  autochrome  plate,  in  which  the 
small  color  elements  were  obtained  by  sifting  potato 
starch  to  obtain  grains  of  approximately  the  same  size, 
staining  up  three  portions  with  the  necessary  dyes, 
then  mixing  and  sifting  over  tacky  glass  until  a  grey 
surface  was  obtained,  any  little  interstices  between 
the  starch  grains  being  filled  up  with  a  black  powder. 
This  film  was  protected  with  an  insulating  varnish 
and  then  a  panchromatic  emulsion  'applied.  A  great 
many  patents  have  been  taken  out  for  the  preparation 
of  similar  plates  and  a  few  have  been  introduced  commer- 
cially, but  so  far  as  the  author  is  aware  the  autochrome 
and  the  Paget  plate  are  the  only  two  that  survive. 

Before  dealing  with  the  practical  working  of  the  proc- 
ess, it  may  be  as  well  to  explain  how  the  colors  are 
formed,  and  for  this  purpose  a  greatly  enlarged  and 
purely  schematic  section  of  a  screen-plate  is  shown  in 
Fig.  17.  On  the  extreme  right  are  the  colors,  or  the 
colored  lights  reflected  from  the  object,  which  meet 
first  the  glass  plate  G,  then  pass  through  the  screen 
elements  S,  to  the  emulsion  film  E. 

It  will  be  seen  that  red  light  can  pass  through  the 
red  element  R  only,  so  that  the  emulsion  is  affected 
by  it  at  this  point  only  and  is  reduced  by  the  developer, 
giving  the  black  patch  shown.  The  same  argument 
applies  to  the  green  and  the  blue  elements;  in  each  case 
we  obtain  the  black  silver  deposit  only  under  the  corre- 
sponding screen  element.  In  the  case  of  yellow,  the  light 
passes  through  both  the  red  and  green  elements,  there- 
fore, we  have  these  blackened  in  the  negative  emulsion. 
The  blue-green  and  crimson  likewise  pass  light  of  two 


138 


COLOR  PHOTOGRAPHY 


colors.  White  light  passes  through  all  three  elements, 
therefore  the  emulsion  is  completely  and  equally  reduced 
1  3  C_  »  S  0 

Bed 

Green 
Blue 


FIG.  17 

under  the  three.  In  the  case  of  black,  that  is,  no  light, 
there  can  be  no  action,  hence  there  is  no  silver  deposit, 
and  in  the  case  of  grey,  which  is  a  mixture  of  black  and 


SCREEN-PLATES  139 

white,  we  again  have  equal  action  but  in  a  lesser  degree. 
It  would  be  possible  to  take  any  number  of  colors  and  treat 
them  in  the  same  way,  but  it  will  be  sufficient  to  take 
two  other  colors,  yellowish-orange  and  brown.  In  the 
former  case,  the  red  is  in  fuU  strength  mixed  with  some 
green,  therefore,  there  is  full  action  under  the  red  and 
some  under  the  green  element;  in  the  case  of  brown, 
which  is  actually  nothing  more  than  reddish-orange 
mixed  with  black,  there  is  also  action  under  the  corre- 
sponding elements.  Assuming  that  our  diagram  thus 
represents  the  result  of  exposure  and  development,  if 
we  should  immerse  the  plate  in  a  fixing  bath,  it  is  ob- 
vious that  we  would  actually  have  a  negative  in  the 
complementary  colors  of  the  subject;  thus,  reading 
down,  the  colors  shown  would  be  blue-green,  crimson, 
red,  green,  black,  white,  grey,  bluish-green  and  a  pale 
greenish-blue.  If  in  any  way  we  should  make  a  posi- 
tive from  this  negative  and  place  it  in  contact  with  the 
same  screen  elements,  we  should  obtain  the  same  colors 
as  those  of  the  object,  as  shown  on  the  left  of  Fig.  17. 
It  is  unnecessary  to  follow  out  the  formation  of  the  colors 
in  the  positive,  as  it  is  obvious  from  the  diagram.  This 
is  the  whole  theory  of  the  screen-plate  process. 

Everyone  knows  that  it  is  extremely  easy  to  distin- 
guish small  objects  as  distinct  when  one  is  fairly  close 
to  them.  As  one  of  the  very  simplest  examples,  we  may 
take  the  case  of  three  trees;  standing  within  about 
twenty  feet,  we  can  not  only  distinguish  each  branch 
but  also  each  leaf,  and  can  tell  from  the  shape  of  the 
latter  whether  they  (the  trees)  are  elms,  oaks  or  beeches. 
But  at  a  distance  of  a  mile  we  no  longer  see  anything 
but  a  general  green  mass,  and  it  would  probably  be  dif- 
ficult to  name  the  trees.  Exactly  the  same  applies  to 


i4o  COLOR  PHOTOGRAPHY 

small  objects:  at  the  distance  of  normal  vision,  about 
ten  inches,  one  can  distinguish  quite  plainly  dots  of 
black  and  white  of  a  diameter  of  about  yV  inch.  At  a 
distance  of  ten  feet  the  dots  appear  to  be  merely  a  grey 
mass,  and  as  we  reduce  the  size  of  the  dots,  or  elements, 
as  we  have  called  them,  the  shorter  becomes  the  dis- 
tance at  which  they  can  be  separated,  until  they  become 
so  small  that  a  microscope  is  required  to  separate  them. 
In  order,  therefore,  for  a  patch  of  color  to  appear  uni- 
form on  a  screen-plate,  the  elements  have  to  be  very  small 
and  in  the  case  of  the  autochrome  they  are  about  0.015 
mm  (0.0024  inch),  therefore  they  are  not  visible  at 
the  distance  of  normal  vision. 

There  are  two  distinct  methods  of  using  this  process. 
If  the  screen  elements  are  of  a  regular  geometrical  pattern, 
regularly  recurring,  then  one  may  use  the  screen-plate 
pressed  into  contact  with  a  separate  panchromatic  plate, 
and  on  development  obtain  a  negative  the  image  of 
which  is  broken  up  into  the  geometrical  pattern.  From 
this  we  can  make  any  number  of  positives  and  by  bind- 
ing them  up  with  similar  screens  in  correct  register, 
we  shall  obtain  a  colored  result.  This  method  is  known 
as  the  separate  method.  But  with  an  irregular  hap- 
hazard mosaic,  such  as  is  formed  in  the  autochrome 
plate,  and  with  elements  of  such  a  fineness,  it  is  an  almost 
hopeless  task  to  fit  the  positive  to  the  screen-plate; 
therefore,  the  emulsion  is  coated  on  the  plate  itself, 
and,  after  development,  the  negative  image  is  dissolved 
away,  leaving  the  unexposed  and  undeveloped  emulsion 
in  situ.  This  is  then  developed  and  gives  us  a  positive 
in  colors.  This  will  be  easily  grasped  from  Fig.  17 A, 
which  shows  the  negative  image  with  the  black  silver 
behind  the  appropriate  color  elements;  if  we  imagine 


SCREEN-PLATES  141 

all  the  white  spaces  there  shown  to  be  covered  by  un- 
developed silver  bromide,  we  have  an  exact  picture  of 
the  developed  autochrome  or  any  other  screen-plate 
by  what  is  known  as  the  combined  method,  that  is,  one 
in  which  the  emulsion  is  coated  on  the  screen-plate  it- 
self. If  now  we  dissolve  the  primary  negative  image, 
it  is  clear  that  we  still  have  our  silver  bromide  under 
the  other  elements,  and  if  this  be  exposed  to  light  and 
developed  we  shall  obtain  the  result  shown  in  Fig.  176, 
and  there  is  no  trouble  in  registration. 

There  are  advantages  and  disadvantages  in  both  meth- 
ods. In  the  combined  method,  if  we  want  more  than  one 
copy  of  a  subject  we  must  obviously  make  more  than 
one  exposure,  whereas,  with  the  separate  process,  having 
once  obtained  the  matrix  negative  we  can  produce 
as  many  copies  as  we  like.  The  combined  method  in- 
volves another  operation,  that  is  the  reversal  of  the  neg- 
ative image  obtained  by  primary  development.  Also, 
if  we  make  a  mistake  and  spoil  the  result,  we  have  lost 
both  screen-plate  and  picture;  while  with  the  separate 
method  our  only  loss  is  the  panchromatic  plate,  and 
the  screen-plate  is  still  intact.  As  to  which  is  the  easier 
process,  this  is  merely  a  matter  of  opinion.  As  regards 
excellence  of  results  there  is  not,  in  the  writer's  opinion, 
anything  to  choose  between  them,  assuming,  naturally, 
that  the  best  results  are  obtained  in  both  cases.  Pos- 
sibly for  the  novice  the  separate  method  is  a  little  the 
easier,  that  is,  if  he  can  make  a  transparency. 

THE  COMPENSATING  FILTER 

In  the  case  of  screen-plate  emulsions,  as  with  all  other 
color-sensitized  ones,  the  characteristic  preponderance 


142 


COLOR  PHOTOGRAPHY 


of  the  activity  of  the  blue  and  violet  rays  still  exists, 
so  that  it  is  necessary  to  insert  between  the  object  and 
its  image  a  correcting  or  compensating  filter,  which  re- 
duces the  rendering  of  the  colors  by  the  plate  to  that 
seen  by  the  eye.  In  Fig.  18  are  shown  two  curves  rep- 
resenting the  luminosity  of  the  spectral  colors  as  seen 
by  the  human  eye  and  by  the  plate,  the  former  being 
marked  V  and  the  latter  P.  As  will  be  seen,  the  peak  of 
the  curve  of  the  latter  is  about  wave-length  4500  in  the 
deep  blue,  whereas  the  visual  luminosity  peak  lies 


550 


450  500 

FIG.  18 


about  wave-length  5500  in  the  yellow-green.  By  an 
error  in  making  the  drawing,  the  wave-lengths  are 
there  given  in  hundreds  instead  of  thousands.  An  extra 
zero  should  be  added  to  each  number  to  make  them 
agree  with  the  text. 

The  filter  that  will  shift  the  plate's  vision  so  as  to 
coincide  with  that  of  the  retina  is  of  a  faint  reddish- 


SCREEN-PLATES  143 

yellow  tinge  and  can  be  made  with  tartrazin,  pheno- 
safranin  and  aesculin.  The  instructions  for  filter  making 
given  in  Chapter  III  must  be  rigorously  followed:  instead 
of  using  the  above  named  dyes,  of  which  the  pheno- 
safranin  has  the  disadvantage  of  rapidly  fading  on  expo- 
sure to  light,  we  may  use  the  more  stable  combination 
of  fast  red  D  and  filter  yellow.  The  density  of  the  first 
named  dyes,  that  is,  the  quantity  per  square  meter  of 
filter  area,  is  tartrazin  0.2  g,  plus  pheno-safranin  0.017  g» 
plus  aesculin  4.0  g.  The  densities  for  the  more  stable 
dyes  are  filter  yellow  0.6  g,  plus  fast  red  D  0.07  g. 

It  is  not  immaterial  where  the  filter  is  placed,  as  it 
has  an  effect  on  the  focus  of  the  lens.  Placed  in  front 
of  the  lens,  it  shortens  the  distance  of  the  plane  focused 
on  by  one-third  of  the  thickness  of  the  filter,  but  as  this 
reduction  of  the  object-plane  is  extremely  small  in  all 
out-door  work  compared  with  the  distance  of  the  object 
it  can  be  ignored.  It  is  only  when  one  reproduces  ob- 
jects, such  .as  a  picture,  or  flowers,  in  something  like 
natural  size  that  it  need  be  taken  into  account.  By 
far  the  best  position  for  the  filter  is  behind  the  lens; 
here  it  is  protected  from  light,  from  accidental  displace- 
ment and  from  injury,  and  it  automatically  makes  its 
own  correction  in  focusing.  In  all  cases  focusing  should 
be  done  with  the  filter  in  position.  As  to  the  method 
of  calculating  the  area  of  the  filter  for  any  given  lens, 
see  Chapter  III.  It  is  extremely  important  that  the 
filter  should  fit  close  to  the  lens,  so  that  no  white  light 
can  creep  around  the  edges  or  be  reflected  from  the  front 
surface  to  any  part  of  the  plate;  for  this  reflected  light 
would  cause  local  or  general  fog,  and  consequent  falsi- 
fication of  the  colors. 

As  in  the  use  of  the  screen-plates  the  glass  is  always 


144  COLOR  PHOTOGRAPHY 

turned  towards  the  lens  and  the  sensitive  surface  away 
from  it,  it  is  clear  that  this  must  be  allowed  for  in  fo- 
cusing. The  matt  side  of  the  ground  glass  should,  there- 
fore, be  reversed  in  position  and  face  outwards,  and  its 
thickness  should  be  that  of  the  screen-plate,  if  critical 
sharpness  is  required.  An  ingenious  idea  that  has  been 
put  forward  is  to  clean  the  emulsion  from  a  spoiled 
plate  and  place  this,  with  the  color  elements  outside, 
in  place  of  the  usual  ground  glass. 

While  directions  have  been  given  for  making  a  filter, 
it  must  be  understood  that  this  is  for  the  autochrome 
plate.  While  it  can  be  used  for  the  Paget  plate,  the 
makers  of  this  issue  special  filters  and  it  is  well  to  purchase 
these.  These  filters  are  adjusted  for  average  daylight, 
and  they  cannot  be  used  successfully  with  any  other 
light,  so  that  special  filters  must  be  prepared  for  these. 
It  may  not  seem  worth  while  to  make  these  filters,  but 
possession  of  a  set  enables  winter  and  evening  work  to 
be  attempted.  The  following  formulas  are,  therefore, 
given  to  complete  the  information. 

For  use  with  Nernst  lamps: 

Gelatine,  i  :  15  solution  40  ccm 

Tartrazin,  i  :  2,500  solution  3  ccm 

To  this  add: 

Aesculin  0.4  g 

Distilled  water  37  ccm 

Ammonia  3  drops 

To  every  100  square  cm  allow  8  ccm  of  the  above 
solution.  The  aesculin  solution  must  be  made  only 
just  before  use.  This  filter  is  combined  with  a  blue 
filter  of  the  following  composition: 


SCREEN-PLATES  145 

Patent  blue,  i  :  1000  solution  2  ccm 

Gelatine,  i  :  15  solution  46  ccm 

Distilled  water  38  ccm 
Allow  7  ccm  per  100  square  cm. 

For  incandescent  gas,  the  same  filters  are  used,  but 
the  quantity  of  the  blue  gelatine  is  reduced  from  7  to 
5  ccm  for  the  same  area. 
For  a  25  ampere  arc: 

Gelatine,  1:15  solution  40  ccm 

Tartrazin,  i  :  500  solution  4  ccm 

Pheno-safranin,  i  :  7000  solution          i  ccm 

Add  to  this: 

Aesculin  0.4  g 

Distilled  water  35  ccm 

Ammonia  3  drops 

Allow  8  ccm  for  the  same  area.  This  filter  is  par- 
ticularly useful  for  photo-micrography  with  screen- 
plates. 

For  flashlight  work,  the  composition  of  the  filter 
will  depend  on  that  of  the  flash  mixture;  Lumiere's 
Perchlora  mixture  is  two  parts  of  magnesium  powder 
and  one  part  of  potassium  perchlorate,  and  for  this  the 
correct  filter  is: 

Gelatine,  i  :  10  solution  40  ccm 

Tartrazin,  i  :  500  solution  5  ccm 

Pheno-safranin  i  :  7000  solution  3  ccm 

To  this  add: 

Aesculin  0.4  g 

Distilled  water  32  ccm 

Ammonia  4  drops 

Allow  8  ccm  per  100  square  cm. 


I46  COLOR  PHOTOGRAPHY 

F.  Novak  suggested  a  mixture  of  two  parts  of  mag- 
nesium and  one  part  of  dry  thorium  nitrate,  and  the 
compensating  filter  for  this  is: 

Gelatine,  i  :  15  solution  100  ccm 

Filter  yellow,  i  :  200  solution  15  ccm 

Crystal  ponceau,  i  :  800  solution  4  ccm 

Water  4  ccm 
Allow  7  ccm  per  100  square  cm. 

EXPOSURE  OF  THE  SCREEN-PLATES 

In  ordinary  black  and  white  photography  it  is  well 
known  that  there  is  a  great  latitude  in  exposure.  One 
may  make  an  error  of  two  or  three  times  one  way  or 
the  other  and  yet  obtain  a  negative  that  will  give  a  good 
result;  but  with  screen-plates  this  is  not  possible.  A 
really  correct  rendering  of  the  colors  is  only  possible 
with  correct  exposure,  this  being  due  to  the  extreme 
thinness  of  the  film  of  emulsion. 

Various  tables  have  been  published  as  guides  for 
the  novice,  but  these  are  not  reproduced  for  the  simple 
reason  that  the  factors  involved  in  estimating  the  correct 
exposure  are  so  delicate  that  they  cannot  be  determined 
from  a  table  with  a  sufficient  degree  of  accuracy.  As 
a  standard  cf  exposure,  the  makers  of  the  autochrome 
plate  state  that  one  second  with  a  lens  working  at  /  :8 
in  summer  and  sunlight  near  the  middle  of  the  day 
is  correct;  but  everyone  knows  that  the  intensity  of  sun- 
light may  vary  enormously.  Then  again,  one  may  wish 
to  take  an  interior,  or  it  may  be  necessary  even  in  sun- 
shine to  use  a  very  small  stop;  theoretically  one  has 
merely  to  increase  the  exposure  in  direct  ratio  to  the 
decrease  in  illumination,  so  that  in  the  case  of  the  dia- 


SCREEN-PLATES  147 

phragms,  assuming  that  one  used  /  :  32  instead  of  /  :  8, 
the  increase  should  be  as  i  :  16,  whereas  actually  it 
would  be  more  like  i  :  24  or  i:  32.  Exactly  in  the  same 
way,  when  working  in  a  comparatively  feeble  light, 
the  increase  in  exposure  does  not  follow  the  usual  law 
that  intensity  of  illumination  and  duration  of  exposure 
are  inversely  proportional.  This  failure  is  well  known, 
but  is  not  often  of  importance  in  black  and  white  work, 
but  with  screen-plates,  in  consequence  of  the  very  low 
practical  sensitiveness  of  the  emulsion,  it  has  to  be 
considered.  The  expression  "practical  sensitiveness" 
is  advisedly  used,  for  that  of  the  autochrome  emulsion 
is  about  36  H.  &•  D.,  but  the  color  elements  cut  this 
down  to  three  and  the  filter  to  one  and  one  half. 

The  most  satisfactory  method,  in  fact,  the  author 
goes  so  far  as  to  say,  the  only  satisfactory  method  of 
determining  exposures  with  screen-plates  is  to  use  one 
of  those  meters  which  measure  the  intensity  of  the  light 
by  the  darkening  of  a  strip  of  sensitive  paper.  The  two 
most  useful  meters  of  this  type  are  those  manufactured 
by  Watkins  and  Wynne,  in  England.  In  these  special 
paper  is  employed,  actually  a  specially  treated  bromide 
and  not  a  printing-out  paper,  and  the  instruments  are 
provided  with  special  scales  that  compensate  for  the 
failure  of  the  above  law.  If  tables  are  useless,  so  also 
are  those  meters  that  gauge  the  light  by  visual  exam- 
ination or  reduction  by  absorbing  material. 

When  the  separate  method  is  used,  one  is  not  tied 
down  to  the  use  of  such  slow  emulsions,  and  may  use 
the  fastest  panchromatic  plates  obtainable;  in  this  case 
the  usual  speed  must  be  adopted  for  use  with  the  meters 
and  the  increase  necessitated  by  the  taking  screen  worked 
out.  It  has  frequently  been  recommended  to  hyper- 


i4 8  COLOR  PHOTOGRAPHY 

sensitize  autochrome  plates  by  bathing  them  in  various 
dye  solutions,  such  as  pinachrome,  etc.;  but  this  is  not 
a  process  that  should  be  attempted  by  the  novice.  A 
special  filter  is  required  and  the  result  is  rarely  correct. 

It  may  be  as  well  to  call  attention  again  to  the  fact 
that  the  screen-plate  must  be  placed  the  wrong  way 
round  in  the  dark  slide,  that  is,  with  the  glass  toward 
the  lens.  It  is  essential,  therefore,  that  the  emulsion 
be  protected  from  damage  by  any  spring  which  keeps 
the  plate  in  register.  The  autochrome  plate  is  issued 
with  a  piece  of  black  card  in  contact  with  the  film,  the 
other  side  being  white,  and  this  should  be  put  in  the 
plate  holder,  back  of  the  plate.  For  the  separate  method 
it  is  imperative  that  the  taking  screen  and  the  sensitive 
emulsion  be  in  as  close  contact  as  possible,  and  it  will 
be  found  that  the  English,  or  book-form  dark  slide,  is 
much  superior  to  the  average  American  plate  holder, 
not  only  in  ease  of  filling,  but  also  in  giving  closer  con- 
tact. Finally,  the  back  of  the  glass  must  be  clean;  any 
dirt  or  finger  marks  will  be  visible  in  the  picture  as  a 
darker  patch.  It  is  easy  to  clean  the  glass  after  loading 
in  the  dark  room,  by  pulling  out  the  sliding  shutter  and 
polishing  with  a  clean  cloth. 

DEVELOPMENT 

The  desensitizing  of  color  plates  has  been  dealt  with 
elsewhere  and  the  same  process  may  be  utilized  for  all 
screen-plate  work.  With  the  separate  method,  the  saf- 
ranin  dyes  may  be  used;  but  for  the  autochrome  plate 
the  makers  advise  the  use  of  the  ammonium  salt  of  au- 
rantia,  in  i  :  2000  solution,  for  one  minute,  as  this  does 
not  delay  the  appearance  of  the  image  nor  prolong 
development  as  does  safranin. 


SCREEN-PLATES  149 

The  original  developer  recommended  for  the  auto- 
chrome  plate  and  applicable  to  all  other  combined  plates 
was  pyro-ammonia,  and  it  is  still  considered  the  best 
by  many  workers.  The  following  solutions  and  method 
are  advised: 

A.  Sodium  bisulphite  solution  3  con 
Pyrogallol  26  g 
Potassium  bromide  26  g 
Water  to  1000  ccm 

B.  Sodium  sulphite,  dry  100  g 
Ammonia,  sp.  gr.  0.880  100  ccm 
Water  to  1000  ccm 

As  the  particular  ammonia  solution  advised  above 
is  not  always  available,  in  America  at  least,  one-fourth 
more  of  the  weaker  solution,  of  specific  gravity  0.9,  should 
be  used.  For  use,  dilute  one  part  of  this  B  solution 
with  three  parts  of  water.  The  above  solutions  are 
mixed  in  the  following  proportions: 

Solution  A  i  part 

Solution  B  diluted  i  part, 

Water  8  parts 

The  duration  of  development  is  dependent  on  the 
tune  of  appearance  of  the  first  sign  of  the  image,  ex- 
clusive of  the  sky  in  landscape  work;  and  the  temper- 
ature of  the  solution  should  be  16°  C.  (60°  F.).  The 
temperature  is  important,  as  any  material  increase 
will  make  the  gelatine  soft,  and  trouble  may  be  caused. 
The  duration  of  development  for  other  temperatures 
may  be  calculated  from  the  following  table,  which  gives 
the  factors  by  which  the  total  time  of  development 
should  be  multiplied  to  obtain  the  same  result: 


150  COLOR  PHOTOGRAPHY 

10°  C.  (50°  F.)  multiply  by  1.6 

16°  C.  (61°  F.)  multiply  by  i.o 

20°  C.  (68°  F.)  multiply  by  0.8 

25°  C.  (77°  F.)  multiply  by  0.6 

The  developer  is  modified  according  to  the  appearance 
of  the  image,  more  of  the  dilute  B  solution  being  added 
in  proportion  to  the  delay  in  its  appearance.  The 
following  table  shows  the  additional  quamtities  of  di- 
lute B  solution  that  should  be  added  to  every  100  ccm: 


Time  of 
appearance  in 
seconds 

Add  diluted 
B  solution 

Total  lime  of 
development  in 
minutes  and  seconds 

22-24 

None 

2 

o 

25-27 
28-30 

2  ccm 
8  ccm 

2 
2 

12 

30 

31-35 
36-41 
42-48 

15  ccm 
20  ccm 
25  ccm 

2 
2 
2 

30 
30 
30 

49-55 
56-64 
65-75 

30  ccm 
35  ccm 
40  ccm 

2 

3 
4 

45 

over  75 

45  ccm 

5 

0 

Almost  any  developing  agent  may  be  used,  the  following, 
however,  in  the  author's  opinion,  being  one  of  the  most 
satisfactory,  as  it  gives  brilliant  results  without  fog: 

Metol  4  g 

Hydrochinon  12  g 

Sodium  sulphite,  dry  50  g 

Potassium  bromide  6  g 

Ammonia,  sp.  gr.  0.92  33  ccm 

Water  to  1000  ccm 


SCREEN-PLATES  1 5 1 

Rodinal,  amidol,  adurol,  metoquinon  and  chloranol 
have  all  been  suggested,  but  as  they  present  no  partic- 
ular advantages,  adherence  to  one  of  the  above  is  advised. 
In  the  separate  method,  in  which  a  panchromatic 
plate  is  used,  one  would  naturally  adopt  the  normal 
developer,  such  as  metol-hydrochinon.  With  these  plates, 
ammonia  should  be  avoided  as  far  as  possible,  and 
it  is  assumed  that  the  worker  knows  how  to  develop 
such  plates.  There  is  only  one  caution  that  need  be 
given,  that  development  should  not  be  prolonged  until 
the  results  are  hard  and  contrasty;  they  should  tend  to 
the  side  of  softness,  and  for  those  who  follow  the  di- 
rections given  on  the  cards  enclosed  with  the  plates, 
the  times  for  "portraits"  should  be  adopted.  Freedom 
from  fog,  as  far  as  possible,  is  desirable,  but  if  the  de- 
sensitizing method  be  adopted  this  need  not  be  feared. 

REVERSAL  OF  THE  IMAGE 

The  preliminary  development  of  the  combined  plate, 
as  has  already  been  explained,  gives  a  negative  image 
in  the  complementary  colors,  and  to  convert  this  into 
a  positive  this  primary  image  is  dissolved.  This  is  ef- 
fected by  treatment  with  acid  potassium  permanganate 
or  acid  bichromate  solution,  and  the  latter  is  on  the 
whole  preferable,  as  the  stock  solution  keeps  better  and 
there  is  no  chance  of  black  spots  being  caused,  which 
may  happen  with  old  permanganate  solution.  The 
latter  should  be  prepared  in  two  solutions,  and  the  per- 
manganate should  be  kept  in  the  dark: 

A.  Potassium  permanganate  4  g 
Distilled  water                          1000  ccm 

B.  Sulphuric  acid,  pure  20  ccm 
Distilled  water  to                     1000  ccm 


iS  2  COLOR  PHOTOGRAPHY 

Mix  in  equal  volumes  immediately  before  use.     The 

bichromate  bath  is: 

Potassium  or  ammonium  bichromate  5  g 
Sulphuric  acid,  pure  10  ccm 

Water  to  1000  ccm 

As  soon  as  development  is  complete,  the  developer 
should  be  poured  off  and  the  dish  filled  up  with  water 
and  gently  rocked  for  a  few  seconds.  The  water  is  then 
poured  off  and  the  dish  again  filled  with  water;  this 
can  be  repeated  three  or  four  times  until  the  plate 
has  been  washed  for  from  thirty  to  forty-five  seconds, 
and  then  the  reversing  solution  can  be  applied.  Plenty 
should  be  used,  and  the  action  should  be  allowed  to  con- 
tinue for  two  or  three  minutes;  then  one  can  turn  on 
white  light  or  go  out  into  daylight.  The  reversing  bath 
should  be  allowed  to  act  not  less  than  five  minutes,  and 
it  is  here  that  so  many  beginners  go  wrong,  in  not  giving 
the  solution  time  enough  to  dissolve  the  primary  image. 
The  author  prefers  to  throw  the  first  lot  of  solution 
away  and  pour  on  fresh  and  allow  to  act  another  three 
minutes.  It  is  not  wise  to  be  economical,  either  hi  time 
or  solution,  at  this  point. 

As  soon  as  the  primary  negative  image  is  dissolved,  the 
picture  hi  colors  will  be  seen  on  looking  through  the  plate, 
as  well  as  the  still  unreduced  silver  bromide  film.  It  has 
been  suggested  that  the  plate,  after  treatment  with  the 
reversing  solution,  should  be  washed  and  dried,  but 
while  this  method  saves  a  little  time  and  trouble  it  should 
not  be  adopted,  as  the  color  rendering  is  never  as  good. 


SCREEN-PLATES  153 

THE  SECOND  DEVELOPMENT 

This  has  the  purpose  of  reducing  to  the  metallic  state 
the  emulsion  which  has  not  been  affected  by  the  primary 
exposure  and  development.  This  reduced  silver  pre- 
vents any  light  from  penetrating  through  the  color  ele- 
ments where  it  should  not,  and  increases  the  brilliancy 
of  the  picture. 

After  the  reversing  solution  has  done  its  work,  the 
plate  should  be  washed  for  a  minute  or  two,  the  easiest 
way  being  to  fill  the  dish  with  water,  rock  gently,  throw 
away  the  water  and  refill,  and  repeat  this  treatment. 
When  dealing  with  the  autochrome  plate  it  must  be 
remembered  that  the  film  is  extremely  tender  and  that 
a  strong  stream  of  water  from  a  tap  may  damage  it. 
The  second  developer  may  be  the  same  as  that  used 
for  the  first  time,  or  the  following  recommended  by 
MM.  Lumiere: 

Sodium  sulphite,  dry  15  g 

Amidol  5  g 

Water  to  1000  ccm 

The  silver  bromide  must  be  exposed  to  white  light, 
such  as  daylight,  to  bring  it  into  a  developable  condition. 
The  plate  should  be  covered  with  the  developer  and  ex- 
posed in  the  dish  to  daylight  until  the  bromide  is  com- 
pletely developed.  If  development  has  been  put  off 
until  evening  one  has  not,  of  course,  daylight  avail- 
able, and  any  white  light  may  be  used,  such  as  gas,  elec- 
tricity or  a  small  piece  of  magnesium  ribbon.  Here 
there  is  no  chance  for  overdevelopment,  but  there  is 
decided  chance  of  underdevelopment,  so  that  one  should 
not  be  in  a  hurry  to  stop  this  process,  and  the  plate 


i54  COLOR  PHOTOGRAPHY 

should  be  exposed  to  white  light  all  the  time.  The 
disadvantage  of  underdevelopment  is  that,  if  the  pic- 
ture is  subsequently  fixed,  any  unreduced  bromide  will 
be  dissolved  and  the  stopping-out  power  of  the  silver 
lowered. 

INTENSIFICATION 

If  the  exposure  is  correct,  and  the  reversal  and  second 
development  properly  carried  out,  there  is  no  need  to 
intensify,  and  the  picture  may  be  considered  to  be 
finished.  But  if  the  picture  appears  weak  it  may  be 
intensified.  The  original  method  was  physical  inten- 
sification with  silver,  for  which  three  solutions  are  re- 
quired: 

A.  Citric  acid  3  g 
Salicylic  acid  0.5  g 
Pyrogallol  3  g 
Distilled  water  1000  ccm 

B.  Silver  nitrate  10  g 
Distilled  water  100  ccm 

C.  Potassium  permanganate  i  g 
Distilled  water  1000  ccm 

While  many  workers  have  experienced  trouble  with  this 
process,  it  is  very  easily  carried  out,  provided  a  few  simple 
points  are  carefully  observed. 

In  the  first  place  the  plate  must  be  free  from  the 
slightest  trace  of  the  second  developer.  To  ensure 
this  it  is  best  to  mix  one  part  of  the  reversing  bath  with 
100  parts  of  water,  then  flood  the  plate  and  rock  not 
longer  than  five  seconds,  and  immediately  pour  off 
and  wash  with  four  or  five  changes  of  water.  The  actual 
intensifier  is: 


SCREEN-PLATES  155 

A  solution  900  ccm 

B  solution  ioo  ccm 

Naturally,  only  enough  will  be  used  to  cover  the  plate; 
the  mixed  solution  should  be  poured  over  the  plate 
and  the  dish  rocked  to  and  fro  for  not  longer  than  thirty 
seconds.  Then  pour  the  solution  away  and  examine 
the  plate  by  transmitted  light;  if  it  looks  brilliant  enough, 
the  plate  may  be  subjected  to  the  clearing  treatment 
described  later;  but  if  not  fresh  intensifier  should  be 
mixed  and  again  applied.  One  of  the  most  frequent 
causes  of  trouble  is  economy  in  this  solution;  this  invari- 
ably leads  to  a  muddy  looking  picture,  as  the  silver  is 
deposited  everywhere,  on  the  fingers,  the  dish  and  those 
parts  of  the  picture  where  it  should  not  be;  it  is  far  better 
to  be  a  little  lavish  and  secure  good  results.  Exactly 
how  far  to  carry  intensification  is  entirely  a  matter  of 
opinion.  The  greater  the  intensification,  the  more 
brilliant  the  colors;  but  it  is  easy  to  overdo  it  and  then 
the  colors  become  glaring,  and  there  is  at  the  same 
time  a  loss  of  the  more  delicate  nuances. 

After  intensification  the  plate  should  be  washed  with 
repeated  changes  of  water  for  not  less  than  one  minute, 
then  flooded  with  the  neutral  permanganate  solution  C 
for  not  more  than  one  minute,  and  again  washed  for 
five  minutes;  it  can  then  be  dried.  Unless  the  plate 
is  properly  washed  after  intensification,  the  acid  in  the 
film  will  cause  the  permanganate  to  dissolve  the  image 
to  some  extent.  Another  cause  of  trouble  is  the  pre- 
cipitation of  minute  crystals  of  silver  in  the  B  solution, 
or  on  the  lip  of  the  bottle,  which  are  washed  off  on 
pouring  out  the  solution.  Care  should  be  taken  not 
to  disturb  any  deposit,  and  it  is  better  to  suck  up 


I56  COLOR  PHOTOGRAPHY 

the  required  quantity  with  a  pipette  from  near  the  top 
of  the  stock. 

As  an  alternative  the  following  method  of  intensi- 
fication may  be  used: 

Cupric  sulphate  20  g 

Potassium  bromide  20  g 

Hydrochloric  acid  5  ccm 

Water  to  1000  ccm 

The  picture  is  bleached  in  the  above,  which  takes  but 
a  minute,  then  rapidly  rinsed  with  three  or  four  changes 
of  water  and  flooded  with  a  five  per  cent  solution  of 
silver  nitrate  to  which  a  few  drops  of  nitric  acid  have 
been  added.  In  fact,  any  intensifier,  except  those  like 
uranium,  which  give  a  colored  deposit,  may  be  used. 

FIXATION  AND  DRYING 

If  the  picture  has  not  been  intensified,  there  is  not 
the  slightest  need  to  fix  it,  but  after  intensification 
it  must  be  fixed,  and  the  following  is  a  suitable  formula: 

Hypo  100  g 

Sodium  bisulphite  solution  50  ccm 

Water  to  1000  ccm 

About  three  minutes  immersion  is  ample,  and  then  it 
can  be  washed  and  dried.  Rapid  drying  of  an  auto- 
chrome  is  important,  as  otherwise  green  patches  may 
make  their  appearance  at  the  edges  of  the  picture,  and 
occasionally  elsewhere.  A  good  plan  is  to  take  hold 
of  the  plate  firmly  by  the  edges  and  then,  with  the  arm 
at  full  length,  jerk  the  plate  rapidly  up  and  down  so  as 
to  sling  off  as  much  water  as  possible.  Then  dry  the 
glass  and,  if  you  have  a  fan,  place  the  plate  at  some  little 


SCREEN-PLATES  157 

distance  from  this  so  as  not  to  have  too  strong  a  draught 
impinging  on  the  film.  If  this  is  not  available,  the  plate 
should  be  placed  film  outwards  against  the  wall  or  sup- 
ported with  the  lower  edge  resting  on  a  few  thicknesses 
of  blotting  paper.  If  the  plate  is  dried  in  a  strong  current 
of  air,  the  film  has  a  tendency  to  curl  at  the  edges,  and 
if  dried  by  heat  there  is  a  very  good  chance  of  the  film 
melting.  In  no  case  must  alcohol  be  used  for  drying, 
as  this  will  invariably  lead  to  one  or  more  of  the  dyes 
being  extracted  from  the  colored  screen-elements,  with 
local  patches  of  incorrect  color  as  the  result.  It  may 
be  taken  as  an  axiom  that  alcohol  must  be  avoided 
with  all  combined  screen-plates. 

VARNISHING  THE  PLATE 

Many  operators  omit  this  operation  altogether,  but 
it  can  be  recommended,  for  not  only  does  it  give  good 
protection  to  the  tender  film  but  it  also  increases  the 
transparency  of  the  picture.  An  excellent  formula  is: 

Gum  dammar  20  g 

Manila  copal,  powdered  50  g 

Carbon  tetrachloride  1000  ccm 

The  mixture  should  be  well  shaken  or  stirred  up  oc- 
casionally during  twenty-four  hours.  Then  the  bottle 
should  be  placed  in  a  water  bath  and  the  temperature 
raised  until  the  solution  boils;  this  should  be  continued 
for  five  minutes  and  the  solution  filtered  while  still  hot. 
This  varnish  dries  rapidly  and  gives  a  colorless  film.  Al- 
coholic, ethereal  or  celluloid  varnishes  must  not  be  used. 
It  is  not  actually  necessary  to  warm  the  plate  before 
varnishing,  but  it  is  preferable  to  do  so,  as  it  drives 
the  last  trace  of  moisture  from  the  gelatine. 


I58  COLOR  PHOTOGRAPHY 

ARTIFICIAL  LIGHT  WORK 

The  extreme  slowness  of  the  combined  screen-plates 
and  the  consequent  long  exposures  in  the  light  of  an 
ordinary  studio  naturally  led  to  experiments  with  flash- 
light mixtures,  with  excellent  results  as  regards  color 
rendering.  The  formulas  for  these  and  the  necessary 
compensating  filters  have  already  been  given.  It  is 
advisable  to  use  a  diffusing  screen  made  of  some  such 
material  as  thin  white  linen  in  front  of  the  flash  lamp; 


FIG.  19 

this  screen  should  be  of  goodly  size,  about  four  and  one- 
half  feet  high  and  three  feet  wide,  and  placed  about 
eighteen  inches  from  the  lamp.  A  suitable  arrangement 
of  the  lamp  and  sitter  is  shown  in  Fig.  19;  in  which  C 
is  the  camera,  R  a  white  reflector,  F  the  background, 
M  the  sitter,  B  the  white  diffusing  screen,  and  L  the  lamp, 
which  preferably  should  be  of  the  type  in  which  the 


SCREEN-PLATES  159 

powder  is  spread  out  in  a  long  tray.  The  quantity  of 
powder  is  dependent  on  the  distance  between  the  lamp 
and  the  sitter,  the  size  of  the  plate  used,  and  the  aper- 
ture of  the  lens.  For  a  3^  x  4^  or  4  x  5  plate,  with  the 
sitter  about  six  feet  from  the  lamp  and  a  lens  working 
at/  :  4.5,  about  eight  grams  should  be  used.  The  lamp 
should  be  rather  higher  than  the  head  of  the  sitter. 

For  flower  and  still  life  work,  magnesium  ribbon 
may  be  used  with  good  effect,  and  if  it  be  burnt  behind 
an  opaque  screen  so  as  to  shield  the  lens,  it  can  be  much 
nearer  the  object  and  less  used.  It  may  be  of  use  to  point 
out  that  three  pieces  of  ribbon,  each  five  inches  long, 
do  not  give  the  same  light  as  one  piece  fifteen  inches  long. 
This  is  probably  due  to  the  long  glowing  ash  of  the  longer 
piece.  For  instance,  setting  the  action  of  four  inches 
of  ribbon  as  one,  that  of  an  eight-inch  piece  was  2.5. 
To  the  photomicrographer  the  screen-plate  process  is 
invaluable,  particularly  in  petrological  work  and  crystal- 
lography with  polarized  light,  and  probably  the  separate 
method  will  commend  itself,  as  from  the  original  negative 
any  number  of  slides  or  prints  may  be  made.  It  is  impos- 
sible to  give  any  useful  hints  as  to  the  exposure,  as  this 
will  depend  on  the  light,  the  numerical  aperture  of  the 
condenser  and  the  objective,  and  the  degree  of  mag- 
nification. As  to  the  filters  to  be  used,  possibly  enough 
on  this  subject  will  be  found  in  the  following  pages. 

FAILURES 

Unfortunately  perfect  immunity  from  failures  cannot 
be  insured,  and  these  are  the  more  serious  because  one 
is  limited  in  remedial  processes,  as  the  color  balance 
is  so  apt  to  be  upset.  Possibly  the  easiest  method  of 


160  COLOR  PHOTOGRAPHY 

dealing  with  the  subject  will  be  to  divide  it  up  into  the 
different  practical  steps. 

Exposure  failures:  General  want  of  sharpness  may  be 
due  to  not  focusing  through  the  filter,  or  to  the  ground 
glass  not  being  reversed,  or  to  the  plane  of  the  latter 
not  being  coincident  with  that  of  the  sensitive  surface. 
This  latter  defect  can  be  remedied  in  future  work  by 
measuring  the  thickness  of  the  screen-plate  and  obtain- 
ing a  ground  glass  of  the  correct  thickness,  or,  as  already 
suggested,  using  a  cleaned-off  plate  for  this;  the  average 
thickness  of  the  autochrome  plate  is  from  1.2  to 
1.8  mm. 

In  the  case  of  the  separate  process,  general  or  local 
want  of  sharpness  may  be  due  to  insufficient  contact 
between  the  taking  screen  and  the  sensitive  plate,  which 
may  probably  generally  be  ascribed  to  want  of  flatness 
in  the  latter. 

If  the  plate  after  the  first  development  is  more  or 
less  black  over  the  whole  surface  and  shows  no  color, 
it  has  been  placed  the  wrong  way  round  in  the  holder, 
that  is,  with  the  sensitive  side,  and  not  the  glass,  toward 
the  lens.  To  avoid  the  occurrence  of  such  an  accident, 
it  is  as  well  after  filling  the  plate  holders  to  draw  up 
the  sliding  shutters  an  inch  or  so,  naturally  working 
at  a  safe  distance  from  the  lamp;  the  reflection  of  the 
light  will  at  once  show  whether  the  glass  is  in  the  correct 
position;  also,  it  looks  black,  whereas  the  sensitive  sur- 
face looks  white. 

The  picture  may  be  very  dense,  with  marked  want 
of  detail  both  in  the  high-lights  and  shadows.  This  is 
caused  by  gross  underexposure  and  insufficient  primary 
development.  There  is  practically  no  remedy,  though 
the  results  can  be  somewhat  improved  by  reduction, 


SCREEN-PLATES  161 

but  this  is  a  delicate  matter,  as  the  thickness  of  the  gela- 
tine is  so  little  that  the  action  of  a  reducer  may  be  too 
violent.  Probably  the  best  reducer  is  made  by  adding 
five  parts  of  the  reversing  solution  to  100  parts  of  water. 
The  reduction  should  be  carried  on  hi  white  light,  and 
close  to  a  water  supply,  so  that  the  moment  enough 
action  has  been  obtained  the  plate  can  be  rapidly  rinsed 
and  the  action  arrested.  If  the  plate  is  rather  too  dense 
in  the  shadows  only,  reduction  may  be  resorted  to  and 
intensification  omitted.  If  the  plate  is  too  heavy  every- 
where and  yet  shows  full  detail,  the  primary  development 
was  a  little  too  short  or  the  temperature  of  the  solution 
was  allowed  to  drop. 

Ill-defined  patches  of  greater  density  than  that  of 
the  picture  as  a  whole  point  to  dirt  on  the  glass,  which, 
by  preventing  access  of  light  to  the  glass,  causes  less  den- 
sity in  the  primary  image  and  consequently  greater 
density  in  the  second  development.  Local  reduction 
may  be  resorted  to,  but  it  is  a  risky  matter. 

A  brilliant  picture,  wanting  in  details  in  the  high- 
lights, is  generally  due  to  too  long  primary  development, 
or  the  reversing  bath  has  been  used  too  long.  There 
is  no  remedy  for  this.  If  the  whole  picture  is  weak  and 
almost  colorless  in  the  shadows  as  well  as  the  high-lights, 
then  overexposure  and  too  long  primary  development 
are  the  cause.  The  only  thing  to  do  is  to  intensify  re- 
peatedly with  the  silver  intensifier.  If  the  picture  looks 
correct  after  intensification,  but  almost  disappears  in 
the  fixing,  either  traces  of  permanganate  were  left  in 
the  film,  which  reacts  with  the  acid  of  the  bath  and  acts 
as  a  reducer,  or  the  second  development  was  not  carried 
far  enough.  The  best  remedy  would  seem  to  be  physical 
development  with  the  following: 


162  COLOR  PHOTOGRAPHY 

Ammonium  sulphocyanide  24  g 
Silver  nitrate  4  g 

Sodium  sulphite,  dry  12  g 
Hypo  sg 

Potassium  bromide  0.5  g 

Distilled  water  100  ccm 

For  use,  add  10  ccm  to  80  ccm  water  and  10  ccm  metol- 
hydrochinon,  rodinal  or  other  developer.  This  solution 
should  be  renewed  as  soon  as  it  gets  muddy.  The  action 
is  rather  slow,  and  if  the  image  appears  whitish,  when 
finished,  it  should  be  bleached  in  a  one  per  cent  solution 
of  mercuric  chloride,  washed,  and  developed  with  an  or- 
dinary developer,  diluted. 

Failures  due  to  the  filter  show  a  more  or  less  blue 
tinge.  If  the  whole  picture  is  blue  or  bluish-green,  then 
the  filter  has  been  omitted  altogether;  stray  white  light 
in  the  camera  also  tends  to  give  this  effect.  There  is 
no  remedy  for  this.  If  the  filter  was  used,  then  one  must 
assume  that  it  has  faded  somewhat,  due  to  careless 
undue  exposure  to  strong  white  light,  or  if  the  filter  is 
home-made,  then  incorrect  quantities  of  the  yellow 
dye  have  been  used. 

When  using  artificial  lights,  too  reddish  pictures 
are  due  either  to  the  use  of  an  improper  filter  or  to 
underexposure.  Because  nearly  all  artificial  lights  have 
an  excess  of  orange  rays  and  are  deficient  in  the  blue, 
the  tinge  of  filters  for  this  work  should  always  be  more  or 
less  greenish  to  cut  down  the  excess  of  orange  and  red. 

Naturally,  undue  exposure  of  the  plate  to  an  unsafe 
darkroom  light  may  cause  fog.  If  this  is  general,  it  is 
caused  by  exposure  of  the  film,  whereas  if  the  glass  has 
been  unduly  presented  to  the  light,  the  latter  may  pene- 


SCREEN-PLATES  163 

trate  the  screen  elements,  and  then  the  general  fog 
is  either  greenish  or  bluish,  according  to  the  color  of 
the  safe-light. 

One  of  the  most  annoying  and  frequent  failures,  es- 
pecially with  beginners,  is  the  appearance  during  the 
second  development  of  negative  patches,  when  the  plate 
is  looked  at.  This  is  particularly  noticeable  in  portraits, 
when  patches  of  black  silver  make  their  appearance 
on  the  cheeks  and  hands  of  the  sitter,  or  sometimes  on 
white  objects,  such  as  a  man's  collar.  This  is  always 
due  to  insufficient  action  of  the  reversing  solution.  Local 
reduction  is  the  only  remedy  for  this. 

Small  black  specks  generally  arise  in  the  manufac- 
ture of  the  plates,  and  are  practically  unavoidable;  on 
the  other  hand,  they  do  not  often  occur  and  are  as  a  rule 
very  small.  Should  they  happen  in  the  shadows  they 
may  usually  be  ignored,  but  in  the  highlights  they 
should  be  touched  with  a  match,  sharpened  to  a  point, 
or  with  a  very  fine  camel-hair  brush,  moistened  with 
the  reversing  solution  or  the  following: 

Potassium  iodide  3  g 

Iodine  i  g 

Water  50  ccm 

As  soon  as  the  spot  disappears,  immerse  the  plate  in 
water,  then  in  the  fixing  bath.  These  spots  are  actually 
metallic  silver  and  the  above  solution  converts  them 
into  silver  iodide,  which  dissolves  in  the  hypo. 

Green  spots  are  due  to  injury  to  the  insulating  var- 
nish between  the  screen-element  layer  and  the  emulsion, 
which  allows  access  of  water  to  the  former,  so  that  the 
green  dye  dissolves.  There  is  practically  no  remedy 
except  local  retouching  with  water-colors,  so  as  to  break 
up  the  area,  but  this  is  unsatisfactory  at  its  best. 


1 64  COLOR  PHOTOGRAPHY 

EXHIBITING  SCREEN-PLATES 

Naturally,  the  use  of  the  screen-plate  for  lantern 
slide  work  presents  great  attractions  and  they  some- 
times form  a  welcome  relief  to  the  black  and  white 
variety.  On  the  other  hand,  they  cannot  be  shown 
at  their  best  along  with  ordinary  slides,  for  as  a  rule 
the  latter  are  shown  on  far  too  large  a  scale  for  all  screen- 
plates.  The  color  elements  absorb  a  great  deal  of  light, 
with  the  result  that,  when  projected  on  too  large  a  scale 
with  an  ordinary  arc  or  lime  light,  they  look  too  dark 
and  a  great  deal  of  their  beauty  is  lost.  It  is,  of  course, 
a  matter  of  personal  opinion,  but  the  author  considers 
that  a  four-foot  picture  is  the  largest  that  should  be 
shown  with  screen-plates.  With  regard  to  the  absorp- 
tion of  the  light,  this  is  over  ninety  per  cent  with  the 
autochrome  and  about  seventy-five  per  cent  with  the 
Paget  plate.  There  is  another  factor  in  the  projection 
of  screen-plates  and  that  is  the  size  of  the  color  elements. 
If  we  take  the  diameter  of  a  lantern  plate  as  four  inches 
and  project  this  on  a  four-foot  disc,  we  have  a  magni- 
fication of  twelve  diameters.  Each  color  unit  is  mag- 
nified in  like  degree,  so  that,  if  they  are  too  large,  they 
will  be  distinctly  visible.  In  the  case  of  the  autochrome 
the  mean  diameter  of  the  elements  is  0.015  mm;  in  the 
case  of  the  Paget  they  are  squares  of  about  0.63  mm  for 
the  blue,  and  0.84  mm  for  the  red  and  green.  If  we  mul- 
tiply these  by  twelve,  we  obtain  0.18  mm  for  the  auto- 
chrome and  1.008  cm  for  the  Paget,  and  it  is  obvious  that 
at  the  normal  distance  of  the  first  row  of  the  audience, 
which  we  may  put  at  ten  feet,  they  will  be  quite  invisible. 
Practically  the  nearest  distance  at  which  the  color  ele- 
ment becomes  visible  at  is  1000  times  its  diameter,  there- 


SCREEN-PLATES  165 

fore  one  can  easily  calculate  the  correct  distance  for  the 
nearest  observers  for  any  degree  of  enlargement. 

Another  important  point  in  the  projection  or  viewing 
of  screen-plates  is  that  the  color  elements  are  adjusted 
to  give  the  best  results  for  a  mean  daylight,  and  the 
color  rendering  is  not  correct  for  any  other  light;  al- 
though we  are  in  the  habit  of  considering  the  projection 
arc  and  lime-light  as  white,  they  are  distinctly  yellow. 
To  obtain  the  best  possible  results,  the  lantern  must  be 
provided  with  a  color  filter,  or  each  slide  bound  up 
with  a  stained  gelatine  plate.  The  latter  method  is 
the  one  which  should  be  adopted  if  the  screen-plates 
are  to  be  shown  in  alternation  with  black  and  white 
slides,  while  if  color  slides  are  to  be  shown  alone,  then 
only  one  filter  need  be  prepared  and  this  should  be  placed 
close  to  the  condenser.  This  correction  filter  can  be 
made  with  rose  Bengal  and  patent  blue,  and  as  similar 
filters  are  required,  as  will  be  seen  later  on,  for  visual 
examination  of  the  pictures,  it  will  simplify  matters 
to  give  the  methods  of  making  these  now. 

In  the  first  place,  three  stock  solutions  should  be 
prepared: 

A.  Gelatine  7  %  solution 

B.  Patent  blue  i  :  1000  solution 

C.  Rose  Bengal  i  :  1000  solution 

For  use  with  an  arc  the  following  quantities  of  the  above 

solutions  are  required  for  one  square  meter  of  filter 
surface: 

Solution  A  300  ccm 

Solution  B  3°  ccm 

Solution  C  3°  ccm 

Water  225  ccm 


1 66  COLOR  PHOTOGRAPHY 

For  oil,  gas,  or  the  old  carbon  filament  electric  lights, 

use: 

Solution  A  300  can 

Solution  B  37.5  ccm 

Solution  C  23  ccm 

Water  225  ccm 

For  incandescent  gas  and  Mazda  lamps  use: 

Solution  A  300  ccm 

Solution  B  23  ccm 

Solution  C  37.5  ccm 

Water  225  ccm 

In  order  to  save  the  trouble  of  coating  with  gelatine 
solution,  some  fixed-out  dry  plates  may  be  immersed 
in  the  dye  solution  mixed  in  the  above  ratios,  using  water 
instead  of  the  gelatine  solution,  for  about  five  minutes, 
then  rinsed  and  the  screen-plates  examined  through 
them  against  the  particular  lights  with  which  they  are 
to  be  used.  One  can  soon  tell  whether  the  plates  require 
deeper  staining  or  reducing  in  color;  the  actual  tint  re- 
quired is  quite  a  weak  one.  The  idea  of  using  these 
tinted  filters  is  to  cut  down  the  excess  of  red  and  green, 
the  patent  blue  cutting  down  the  former  and  the  rose 
Bengal  the  latter.  Other  dyes  with  similar  absorptions 
may  be  used;  but  in  all  cases  the  filters  must  be  dry  be- 
fore the  pictures  are  examined,  as  with  many  dyes  the 
tints  change  considerably  in  drying. 

To  increase  the  brilliancy  of  the  pictures  it  has  been 
suggested  that  aluminum  screens  be  used,  and  they  cer- 
tainly are  an  improvement  for  narrow  rooms  and  halls; 
but  in  theatres  of  greater  width  the  audience  at  the 
sides  has  a  less  satisfactory  view  than  when  ai\  ordinary 


SCREEN-PLATES  1 6  7 

screen  is  used.  For  home  exhibitions,  ordinary  Bristol 
cardboard  forms  an  excellent  screen,  or,  if  the  room  is 
long  enough  to  permit  of  the  lantern  being  placed  behind 
the  screen,  a  sheet  of  ground  glass  or  white  sheeting 
or  pure  white,  not  blue-white,  tracing  cloth  stretched  over 
a  frame  may  be  used. 

For  viewing  in  the  hand  a  viewing-frame  has  become 
very  general.  This  is  nothing  more  than  a  mirror  placed 
horizontally,  with  a  wooden  or  metal  frame,  at  an  angle 
of  45  degrees,  with  an  aperture  for  the  picture.  Side  wings 
of  cloth,  card  or  black  material  prevent  side  light  from 
reaching  the  mirror,  which  is  placed  flat  on  the  table, 
the  picture  being  viewed  in  the  mirror.  Naturally  the 
picture  is  placed  upside  down  and  inside  out,  that  is,  with 
its  picture  side  away  from  the  mirror.  In  all  cases  the 
pictures  should  be  protected  by  a  cover  glass  and  bound 
up  like  an  ordinary  slide.  For  showing  at  exhibitions, 
it  is  better  to  arrange  them  in  frames,  so  that  no  white 
light  can  creep  round  the  edges,  and  use  the  long  line- 
o-lite  electric  lamps,  placing  these  at  the  top  and  bottom 
of  the  rows  of  pictures,  with  asbestos  or  metal  backing 
painted  white,  arranged  so  that  no  light,  except  that 
passing  through  the  pictures,  can  reach  the  eyes.  This 
arrangement  enables  them  to  be  shown  at  night  and  also 
makes  one  entirely  independent  of  daylight,  which  is 
sometimes  difficult  to  reflect  so  as  to  give  even  illumi- 
nation. To  prevent  access  of  daylight  to  the  front  of 
the  pictures,  battens  may  be  run  out  over  the  top  of 
the  frames  and  black  cloth  nailed  to  them,  the  extent 
to  which  the  battens  should  project  being  determined 
by  the  position  of  the  windows  of  the  gallery.  Side 
wings  at  the  end  of  each  row,  and  within  it  if  it  is  very 
long,  are  also  needed. 


1 68  COLOR  PHOTOGRAPHY 

PRINTING  FROM  SCREEN-PLATES 

Having  obtained  a  color  picture  by  means  of  a  screen- 
plate,  one  naturally  wants  to  print  from  it,  and  we  can 
divide  this  subject  into  two  distinct  parts;  first,  the 
production  of  another  screen-plate,  and  secondly,  the 
production  of  paper  prints. 

As  regards  the  first,  we  may  dismiss  the  separate 
method  in  very  few  words,  as  it  merely  entails  the 
making  of  other  black  and  white  transparencies  and 
binding  them  up  with  the  viewing  screens.  But  in  the 
combined  processes,  the  reproduction  on  another  plate 
involves  some  little  difficulties. 

At  the  outset  it  must  be  recognized  that  an  abso- 
lutely faithful  reproduction  is  out  of  the  question.  The 
second  picture  must  always  be  contaminated  with  black, 
that  is,  the  colors  are  of  lowered  luminosity.  On  the 
other  hand  the  results  are  not  displeasing,  and  if  the 
original  is  not  at  hand  to  be  compared  with,  no  one  is 
any  the  wiser.  The  most  satisfactory  method  of  re- 
producing an  autochrome  by  contact  is  that  devised 
by  the  Lumieres,  and  if  carefully  followed  the  failures 
are  few;  the  necessary  apparatus  can  be  easily  knocked 
up,  even  of  cardboard.  A  rectangular  light-tight  box 
A,  B,  C,  D,  (Fig.  20),  40  cm  (16  in.)  in  length  is  required, 
which  should  be  painted  dead  black  inside,  to  prevent 
reflections.  At  one  end  is  cut  an  aperture,  in  which  is 
placed  a  special  compensating  filter  E,  the  composition 
of  which  has  been  given  in  connection  with  flash-light 
work.  This  must  be  arranged  so  that  no  white  light 
can  creep  around  the  edges.  At  the  other  end  is  placed 
a  plate-holder,  a  printing  frame  or  some  similar  arrange- 
ment, which  also  must  be  light-tight.  In  this  is  placed 


SCREEN-PLATES 


169 


the  picture  to  be  reproduced,  with  its  glass  toward  the 
inside  of  the  box,  and  behind  the  picture  is  placed  the 
autochrome  plate,  with  its  glass  in  contact  with  the  film 
of  the  picture;  behind  is  placed  the  usual  black  card. 
G  is  a  block  of  wood,  or  other  support,  preferably 
weighted  at  the  bottom,  so  that  it  will  not  tip  over,  and 


FIG.  20 


into  the  top  is  screwed  an  ordinary  brass  electric  binding 
screw.  5  is  a  spiral  of  iron  wire;  G  must  be  so  placed 
that  the  spiral  of  wire  is  opposite  the  center  of  the  filter, 
and  about  5  cm  from  it.  The  spiral  should  be  formed 
by  coiling  iron  wire  round  a  cylindrical  rod  of  3  or  4  mm 
diameter,  as  closely  as  possible,  and  then  slightly  pulling 
it  out  until  the  coils  of  the  spiral  are  separated  by  about 
i  cm.  This  is  merely  the  holder  for  the  magnesium 
ribbon  that  is  used  as  the  illuminant.  Copper  or  brass 
wire  must  not  be  used  for  the  spiral. 

The  required  length  of  magnesium  ribbon  is  cut  off, 
and  this  will  naturally  depend  on  the  density  of  the 
picture;  with  ribbon  of  2.6  mm  width,  which  is  about 
the  average,  from  10  to  20  cm  will  be  needed.  It  should 
be  folded  end  to  end  and  then  placed  edgewise  in  the 
spiral.  An  opaque  card  or  something  that  will  act  as 


1 70  COLOR  PHOTOGRAPHY 

a  shutter  must  be  placed  over  the  filter  aperture;  a  good 
sized  book  that  will  stand  up  on  its  edge  is  handy.  The 
ends  of  the  ribbon  can  then  be  ignited  by  means  of  a 
candle  or  spirit  lamp,  the  shutter  removed  from  in  front 
of  the  filter,  and  the  exposure  made.  The  plate  is  then 
treated  exactly  as  though  it  had  been  exposed  in  the 
camera. 

No  definite  data  can  be  given  as  to  the  length  of  ribbon 
required,  but  one  can  tell  from  the  results  as  to  whether 
under  or  overexposure  has  been  given,  and  this  will  be 
a  guide  in  future  work.  It  is  important  to  have  the 
ribbon  standing  on  its  edge  in  the  spiral,  as  if  lying  flat 
it  may  go  out. 

Obviously  one  can  use  the  camera  and  either  enlarge 
or  reduce  the  size  of  the  picture;  but  as  the  color  elements 
are  also  enlarged  at  the  same  time,  there  is  obviously 
a  limit  beyond  which  one  should  not  go.  Precisely 
the  same  arrangement  as  just  described  may  be  used 
for  the  illumination.  The  lens  of  the  camera  takes  the 
place  of  the  printing  frame  and  the  connection  between 
the  illuminating  box  and  the  lens  should  be  made  light- 
tight,  which  can  be  easily  done  with  a  cloth. 

It  is  possible  to  reproduce  an  autochrome  by  means 
of  a  Paget  screen-plate,  and  thus  obtain  a  negative  from 
which  any  number  of  transparencies  can  subsequently 
be  made;  one  may  proceed  exactly  as  described  above, 
only  substituting  the  Paget  taking  screen  and  panchro- 
matic plate  for  the  autochrome. 

It  will  be  found  most  convenient  to  carry  out  these 
operations  in  the  dark  room,  and  further  it  may  be  said 
that  in  no  case  should  daylight  be  used  as  the  illuminant, 
as  its  composition  varies  so  much  that  false  color  ren- 
dering is  almost  certain.  Other  illuminants  than  mag- 


SCREEN-PLATES  171 

nesium  may  be  used,  but  in  every  case  the  special  filter 
must  be  used.  Magnesium  is  cheap  and  handy  and  its 
composition  always  constant,  so  that  it  is  by  far  the 
most  convenient. 

As  regards  the  reproduction  of  screen-plates  in  colors 
direct  on  paper,  the  only  method  of  doing  this  is  by  the 
bleach-out  process,  which  is  described  later,  and  it  can 
not  be  recommended.  The  paper  has  to  be  prepared 
and  the  results  are  not  worth  the  trouble  involved,  es- 
pecially as  they  are  not  permanent  and  rapidly  fade 
in  light. 

To  prepare  permanent  prints  from  screen-plate  pic- 
tures, one  must  have  recourse  to  one  of  the  tri-color 
sub  tractive  methods  already  described;  to  utilize  these 
it  is  obvious  that  we  must  have  the  three  constituent 
negatives,  but  these  are  not  difficult  to  make.  The  first 
requisite  is  a  set  of  sharp-cutting  filters,  the  purpose  of 
which  is  to  isolate  each  individual  color,  that  is  all  the 
red,  all  the  green,  and  all  the  blue.  These  filters  must 
be  of  such  a  nature  that  they  transmit  only  the  light 
of  one  color.  They  can  be  made  without  much  trouble 
and  as  they  are  not  used  except  as  light  screens,  they 
need  not  be  made  with  such  careful  attention  to  par- 
allelism of  surfaces,  or  cementing,  as  is  necessary  in  the 
case  of  lens  filters.  It  will  in  fact  be  more  convenient 
to  make  them  the  full  size  of  the  pictures. 

The  red  filter  can  be  made  from  two  glasses,  one  coated 
with  methyl  violet  and  the  other  with  rose  Bengal  and 
tartrazin,  or  crystal  violet  and  tartrazin.  The  rose  Ben- 
gal filter  is  made  from: 

Tartrazin  10  g 

Rose  Bengal  5  g 

Gelatine,  8  per  cent  solution  700  ccm 


I7 2  COLOR  PHOTOGRAPHY 

The  methyl  violet  is: 

Methyl  violet  0.7  g 

Gelatine  solution  700  ccm 

The  crystal  violet  is: 

Crystal  violet  0.4  g 

Tartrazin  5.0  g 

Gelatine  solution  700  ccm 

The  above  quantities  are  sufficient  for  i  square  meter. 
It  is  not  advisable  to  mix  the  violet  with  the  rose  Bengal. 
A  few  drops  of  glacial  acetic  acid  may  be  used  with  both 
the  violets  to  facilitate  solution.  Unless  the  dyes  are  used 
in  the  form  of  a  solution  previously  made,  care  must 
be  exercised  that  they  are  actually  in  solution.  There 
should  be  no  difficulty  in  this,  as  they  are  readily  soluble 
in  the  hot  gelatine,  only,  if  added  all  at  once,  small 
lumps  of  the  dyes  may  become  coated  on  the  outside 
with  chilled  gelatine  and  may  therefore  not  dissolve 
well.  It  is  preferable  to  make  the  gelatine  solution 
double  strength,  use  half  of  the  water  to  dissolve  the 
dyes,  and  then  mix.  The  dyed  gelatine  should  be  fil- 
tered through  linen  that  has  been  well  washed  and  wrung 
out  of  hot  water. 

The  green  filter  must  be  made  with  two  glasses;  one 
should  be   coated   with: 

Tartrazin  2  g 

Naphthol  green  i  g 

Gelatine,  8  per  cent  solution  700  ccm 

and  the  other  is  coated  with: 

Acid  green  JE  0.5  g 

Gelatine  solution  700  ccm 


SCREEN-PLATES  173 

In  place  of  the  acid  green,  3.0  g  of  brilliant  green  may 
be  used. 
The  blue  filter  is  prepared  with: 

Yellowish  eosin  4.0  g 

Gelatine,  8  per  cent  solution  700  ccm 

3.0  g  bluish  eosin  may  be  used  instead  of  the  yellowish. 
The  second  glass  is  coated  with: 

Methylene  blue  46  i  g 

Gelatine  solution  700  ccm 

For  those  who  do  not  want  the  trouble  of  making  the 
niters,  the  Wratten  &  Wainwright  gelatine  film  filters  of 
the  requisite  size  may  be  bound  up  between  glasses.  The 
numbers  of  their  filters  are,  for  the  red  No.  29  or  F, 
for  the  green  No.  61  or  N,  and  for  the  blue  No.  50  or  L. 
A  moment's  consideration  will  show  us  that  as  we 
want  to  reproduce  the  red,  we  must  use  a  red-sensitive 
plate,  and  it  will  be  found  more  satisfactory  to  use  pan- 
chromatic plates  for  all  three  negatives,  as  by  doing 
so  the  gradation  in  the  three  negatives  will  be  more 
alike  than  when  we  use  different  kinds.  There  is  some 
latitude  here,  as  we  are  able  to  modify  the  final  result, 
and  one  might  choose  a  panchromatic  for  the  red,  an 
isochromatic  for  the  green  and  an  ordinary  plate  for  the 
blue  filter  exposures;  but  it  cannot  be  advised.  Whether 
a  fast  or  slow  panchromatic  plate  be  used  is  of  no  par- 
ticular moment;  the  slow  kind  will  give  as  good  results 
as  the  fast  and  is  less  likely  to  fog.  At  the  same  time 
it  must  be  borne  in  mind  that  we  are  making  negatives, 
not  transparencies,  and  this  must  be  kept  in  view  in 
developing.  Brilliant-looking  plates  with  clear  glass 
shadows  are  not  the  desideratum;  but  soft  negatives, 


i74  COLOR  PHOTOGRAPHY 

rather  thin  in  the  high-lights,  with  fully  exposed  shadows, 
should  be  aimed  at.  It  is  immaterial  what  developer  is 
used,  and  the  beginner  should  use  that  to  which  he  is 
accustomed.  Naturally  the  desensitizing  process  may 
be  adopted,  and  the  plates  should  be  backed. 

In  the  reproduction  of  a  screen-plate  it  is  clear  that 
we  might  place  it  with  the  film  in  contact  with  the  sen- 
sitive plate.  Then  we  should  have  the  color  elements 
reproduced  quite  sharp,  and  every  negative  would  be 
broken  up  into  minute  dots  corresponding  in  size.  For 
some  positive  processes  this  might  not  be  a  disadvantage, 
but  in  the  case  of  the  separate  system  in  which  the  posi- 
tive is  bound  up  with  a  viewing  screen,  we  cannot  ob- 
tain contact  with  the  sensitive  surface.  The  result  will 
be  more  or  less  want  of  sharpness,  but  this  will  not  be 
of  serious  moment,  and  it  breaks  up  the  screen  pattern, 
so  that  almost  closed  or  continuous  tone  negatives  are 
obtained.  Actually  it  is  advisable  to  follow  the  same 
plan  with  an  autochrome,  that  is,  to  interpose  between 
the  sensitive  surface  and  the  picture  film  a  colorless 
transparent  medium  of  greater  or  lesser  thickness. 

There  are  some  very  simple  mathematical  formulas 
by  which  we  can  tell  not  only  what  ought  to  be  the  thick- 
ness of  the  intervening  medium,  but  also  the  distance 
of  the  light  source,  and  the  resulting  want  of  sharpness 
in  the  resulting  negatives.  But  one  of  the  main  ideas 
in  this  little  book  has  been  to  avoid,  as  far  as  consistent 
with  clarity,  mathematics  and  deep  theory,  so  that  it 
will  be  assumed  that  it  is  required  to  make  the  negatives 
from  autochrome  and  Paget  pictures.  A  camera  may 
be  used  and  it  should  be  racked  out  to  50  cm.  If  this 
is  not  possible,  then  the  simple  device  given  on  p.  169 
should  be  used,  and  it  will  be  assumed  that  it  is  required 


SCREEN-PLATES  175 

to  enlarge  the  screen  elements  so  that  they  just  close 
up.    Then  the  size  of  the  light-source  is  found  by  the 
following    simple    rule: 
Size  of  light  = 
Element-size  X  Enlargement  —  i  X  Camera  Extension 

Separation-thickness 

The  degree  of  enlargement  to  cause  the  image  to  coal- 
esce is  taken  as  4,  the  camera  extension  is  set  at  500  mm, 
the  separation  thickness  is  that  of  the  autochrome,  which 
is  approximately  2  mm,  and  the  size  of  the  element  is 
taken  as  0.025  mm,  so  that  we  have: 

Light  size  =  0.025  — =  18  mm 

Now  the  aperture  in  the  box,  where  the  comple- 
mentary filter  was  placed,  and  which  can  now  be 
replaced  by  the  sharp-cutting  filters,  is  actually  the 
source  of  light,  therefore,  we  merely  have  to  cut  a 
card  with  a  circular  aperture  of  18  mm  in  diameter 
and  place  over  it  a  ground  glass  to  obtain  the  required 
effect. 

In  the  case  of  the  Paget  plate,  we  may  take  the  size 
of  the  color  element  as  0.115  mm>  and  the  thickness 
of  the  viewing  screen  as  0.5  mm.  Then  we  have: 

(4  -  i)  X  500 
Light-size  =  0.115 =  115  mm 

If  this  size  is  too  large  to  be  convenient,  and  it  might 
be  if  the  camera  were  used,  then  the  thickness  of  the 
glass,  or  the  distance  between  the  two  films,  is  found 
from  the  simple  equation: 

Camera  Length 

Separation-thickness  =  — ,  T  .  ,  ,    X  (Size  of  En- 
Size  of  Light 


176  COLOR  PHOTOGRAPHY 

largement  -  i)  X  Size  of  Element.  So,  if  we  set  the 
size  of  the  light  at  50  mm,  then: 

500 
Separation  =  —  x  (4  -  i)  X  0.115  =  345  mm 

When  using  the  camera,  the  lens  should  be  removed 
and  the  ground  glass  put  in  its  place,  with  an  opaque 
card  of  the  correct  aperture.  If  the  aperture  is  larger 
than  the  lens  flange,  then  the  lens  board  may  be  removed, 
which  is  usually  possible. 

Magnesium  ribbon  will  be  found  the  most  convenient 
light-source.  It  may  occur  to  the  reader  that  this  is 
really  a  very  small  source  of  light:  but  actually  the 
ground  glass  becomes  the  light,  and  it  is  easy  with  mag- 
nesium to  evenly  illuminate  such  a  relatively  small 
area.  Daylight  may  be  used,  and  the  camera  should 
then  be  pointed  direct  to  a  white  cloud  or  a  white  sky, 
not  a  blue  sky. 

It  is  unnecessary  to  enter  into  any  further  particulars 
than  have  already  been  given  as  to  the  printing  pro- 
cesses. The  same  rules  apply,  and  the  so-called  com- 
plementary colors  must  be  used  for  printing. 

STEREOSCOPIC  WORK  WITH  SCREEN-PLATES 

The  combination  of  stereoscopy  and  color  would  seem 
almost  ideal,  and  should  present  no  particular  difficul- 
ties to  the  expert  worker  in  stereoscopy.  But  there  are 
one  or  two  points  that  it  may  be  as  well  to  explain.  Nat- 
urally, if  the  separate  system  is  adopted  and  two  sep- 
arate plates  are  used,  no  advice  is  needed,  as  it  is  a  simple 
matter  then  to  obtain  the  right-hand  picture  for  the 
right  eye  and  the  left-hand  picture  for  the  left  eye.  But 
when  we  use  a  long  plate  on  the  combined  system  (and 


SCREEN-PLATES  177 

this  is  the  only  way  to  get  correct  results  as  regards  even- 
ness), the  matter  is  not  so  simple.  It  would  seem  that 
one  might  merely  turn  the  plate  longways  with  the  glass 
toward  the  eyes,  and  the  result  should  be  correct.  As 
a  matter  of  fact,  one  does  get  relief;  but  it  is  not  stereo- 
scopy,  but  pseudo-stereoscopy,  that  is  to  say,  the  more 
distant  objects  stand  out  in  front  of  the  near  ones.  It 
is  a  curious  fact  that  many  people  cannot  see  this  until 
it  is  pointed  out.  There  is  also  another  point  that  not 
all  people  can  see,  and  that  is  that  the  color  elements 
appear  on  different  planes,  so  that  instead  of  having 
red  and  green  dots  side  by  side,  the  red  appear  farther 
away.  This  is  particularly  apparent  when  the  lenses 
of  the  stereoscope  magnify,  and  is  primarily  due  to  the 
want  of  achromatism  of  the  eye.  It  can  be  lessened 
by  using  lenses  of  longer  focus. 

It  will  be  assumed  that  the  worker  knows  the  ordinary 
rules  of  mounting  stereoscopic  pictures,  that  the  separa- 
tion of  objects  should  be  approximately  82  mm,  and 
the  total  length  of  the  pictures  should  be  180  mm.  Then 
it  will  be  found  as  a  rule  that  part  of  each  picture  must 
be  cut  off.  The  cutting  of  an  autochrome  plate  is  not 
an  easy  matter  until  you  know  how:  for  if  the  glass 
is  cut  in  the  usual  way  and  then  snapped  it  is  ten  chances 
to  one  that  the  screen-film  will  tear  irregularly  and  the 
plate  be  completely  spoiled. 

The  proper  way  to  set  to  work  is  to  place  the  picture, 
film  up,  on  a  flat  support,  and  then  with  a  straight  edge 
and  a  sharp  penknife  cut  right  through  the  gelatine  and 
screen-film  down  to  the  glass,  about  one-sixteenth  of 
an  inch  on  either  side  of  the  middle  dividing  line.  Then 
turn  the  plate  over  and  with  the  aid  of  the  straight 
edge  cut  the  glass.  But,  as  it  is  not  easy  to  see  the  di- 


178  COLOR  PHOTOGRAPHY 

viding  line,  the  best  way  to  go  to  work  is  to  draw  a 
straight  line  on  a  sheet  of  card  or  paper,  set  the  straight 
edge  to  this  and  with  the  diamond  draw  another  line, 
bearing  rather  heavily.  The  cutting  point  of  the  dia- 
mond will  mark  the  card  and  give  a  gauge  by  which  to 
cut,  for  if  the  dividing  line  be  made  to  coincide  with  the 
pencil  mark,  which  must  be  longer  than  the  width  of  the 
plate,  the  diamond  line  will  be  the  position  of  the  straight 
edge.  It  is  advisable  to  rule  the  diamond  line  in  pencil 
also  so  that  it  may  be  seen  projecting  beyond  the  edges 
of  the  plate.  If  the  cut  then  be  properly  made  so  as 
to  fall  between  the  cuts  through  the  film,  the  glass  may 
be  snapped  without  the  film  tearing  except  at  the  cuts. 
The  distance  of  the  diamond  must  be  found  for  each 
tool,  as  they  differ  slightly,  but  the  normal  working 
distance  is  about  2  mm. 

The  pictures  having  been  cut  and  transferred,  the  film 
sides  should  face  the  observer,  and  the  plates  may  be 
stuck  down  to  a  glass  with  a  little  dab  of  seccotine  or 
other  stickfast  at  each  corner,  then  masked  and  a  cover 
glass  bound  up.  Possibly  it  should  be  pointed  out  also 
that  the  longer  the  focus  of  the  camera  lenses  the  better, 
and  that  1 8  to  25  cm  is  better  than  the  usual  9  to  15  cm, 
as  the  illumination  at  the  margins  of  the  pictures  is  better, 
and  too  large  a  diaphragm  should  not  be  used. 


CHAPTER  XIII 

THE  BLEACH-OUT  PROCESS 

AS  a  laboratory  experiment  this  is  an  extremely 
interesting  process,  but  from  the  practical  point 
of  view  it  is  not  worth  wasting  an  hour  over,  in  the 
present  state  of  our  knowledge.  It  was  originally  sug- 
gested by  Ducos  du  Hauron  and  Chas.  Cros  from 
purely  theoretical  reasoning  and  lay  dormant  from  that 
time,  1867,  until  1895,  when  it  was  put  into  practical  use. 
The  principle  of  the  process  is  based  on  what  is  known 
as  the  Grotthus-Draper  law,  which  is,  that  only  light 
which  is  absorbed  can  exert  chemical  action;  this  may 
be  extended  and  amplified  by  stating  that,  as  only  com- 
plementary colors  are  absorbed,  it  is  only  these  that 
can  act  on  a  colored  substance. 

Briefly  put,  three  fugitive  aniline  dyes,  red,  yellow, 
and  blue,  are  mixed  together  in  suitable  proportions, 
so  as  to  give  a  neutral  grey  tint.  If  such  a  film  be  ex- 
posed to  white  light  they  will  all  fade  and  we  shall  see 
the  white  support;  but  if  exposed  to  colored  light,  then 
the  limitation  already  pointed  out  as  to  the  comple- 
mentary colors  comes  into  play.  Under  a  red  glass,  the 
blue  and  yellow  dyes  fade,  as  together  they  make  green; 
under  green  glass,  the  red  fades,  as  this  is  comple- 
mentary to  green;  under  the  blue,  the  yellow  and  red 
fade  out,  leaving  only  the  blue.  The  action  of  any  in- 
termediate color  is  explicable  in  the  same  way,  black 
being,  of  course,  formed  by  none  of  the  dyes  fading.  It 
179 


i8o  COLOR  PHOTOGRAPHY 

is  clear,  then,  that  we  must  start  with  a  colored  origi- 
nal, and  for  purely  experimental  work,  nothing  is  better 
than  pieces  of  stained  gelatine  bound  up  with  glasses. 

A  great  deal  of  experimental  work  has  been  done  on 
this  process,  and  bleach-out  paper  was  for  a  few  years 
a  commercial  article.  Unfortunately,  while  great  ad- 
vances have  been  made  in  the  rapidity  of  the  bleaching, 
it  has  not  yet  been  possible  to  find  any  real  fixing  agent, 
that  is,  any  substance  that  will  prevent  the  dyes,  forming 
the  image,  from  still  further  bleaching.  So  the  results, 
when  exposed  to  white  light,  gradually  fade  out. 

Exact  formulas  cannot  be  given,  as  so  much  depends 
on  the  dyes;  but  sufficient  may  be  told  to  lead  the  ex- 
perimenter on  the  right  road.  Unfortunately,  the  prep- 
aration of  the  paper  direct  is  not  satisfactory,  as  the 
dyes  have  a  tendency  to  wander  or  migrate  into  the 
paper  itself,  so  that  most  of  the  best  results  have  been 
obtained  by  coating  on  opal  glass,  whence  the  film  is 
stripped.  If  it  is  not  desired  to  use  this,  then  gelatin- 
ized paper  may  be  used;  this  can  be  prepared,  as  has 
already  been  suggested,  by  fixing  out  bromide  or  other 
paper,  and  hardening.  The  plan  already  proposed 
of  stretching  the  paper  may  also  be  adopted. « 

To  prepare  the  dyed  gelatine,  the  following  solutions 
should  be  made  up:  methylene  blue  BB,  2  per  cent  solu- 
tion in  water;  auramin  concentrated,  2  per  cent  solu- 
tion in  alcohol;  bluish  erythrosin,  0.5  per  cent  solution 
in  water.  Soft  emulsion  gelatine  and  hydrogen  peroxide 
will  also  be  required.  There  are  two  methods  of  prepar- 
ing the  paper;  either  the  paper  is  immersed  in  an  ethereal 
solution  of  hydrogen  peroxide,  or  an  aqueous  solution  of 
the  peroxide  is  used  to  make  the  gelatine  solution.  Deal- 
ing with  the  former  method  first,  prepare  a  solution  of: 


THE  BLEACH-OUT  PROCESS  181 

Soft  gelatine  100  g 

Distilled  water  1000  ccm 

Allow  the  gelatine  to  soak  for  about  15  minutes,  then 
melt  by  the  aid  of  a  water  bath,  and  divide  into  three 
portions.  To  one,  add  40  ccm  of  methylene  blue  solu- 
tion; to  the  second  lot  add  20  ccm  of  the  auramin  solu- 
tion, and  to  the  third  15  ccm  erythrosin  solution.  Then 
add  the  yellow  solution  to  the  blue,  and  finally,  with 
constant  stirring,  gradually  add  the  red  solution.  To- 
wards the  end  this  red  solution  must  be  added  very  grad- 
ually, and  after  each  addition,  a  drop  of  the  mixture 
should  be  placed  on  white  paper.  As  soon  as  a  faint 
reddish  tinge  is  apparent,  the  addition  of  the  red  must 
be  stopped;  the  main  color  must  be  grey. 

Now  keep  the  dyed  gelatine  at  a  temperature  of  about 
40  °  C.  (104  °  F.)  for  from  four  to  five  hours;  then  filter, 
and  it  is  ready  for  coating.  If  the  paper  has  been 
stretched  on  glass  it  can  be  treated  exactly  like  a  plate 
which  is  to  be  collodionized,  that  is,  supported  on  the 
back  with  a  rubber  bulb,  the  dyed  gelatine  poured  on 
and  the  plate  inclined  until  the  surface  is  covered,  and 
then  put  on  a  level  slab  to  set.  If  it  is  to  be  coated  by 
floating,  then  the  gelatine  must  be  poured  out  into  a 
dish,  any  air  bubbles  broken  or  led  to  the  sides,  the  paper 
bent  into  the  form  of  a  J  and  the  bottom  of  the  loop 
carefully  lowered  on  to  the  surface  at  one  end  of  the  dish, 
with  the  short  end  of  the  loop  pointing  towards  the 
middle  of  the  dish,  and  the  other  end  slowly  lowered 
and  the  paper  allowed  to  slide  along  the  surface  of  the 
gelatine.  With  a  little  practice  this  can  be  done  without 
forming  any  air  bubbles.  As  soon  as  the  paper  begins 
to  curl  at  the  edges,  it  should  be  slowly  drawn  off  the  sur- 


182  COLOR  PHOTOGRAPHY 

face  and  immediately  turned  over  on  to  a  flat  plate 
to  set.  The  temperature  naturally  plays  a  great  part 
in  determining  the  quantity  of  gelatine  that  adheres 
to  the  paper;  the  lower  it  is,  the  thicker  the  film.  From 
35  °  to  38  °  C.  (95  °  to  100  °  F.)  is  a  good  range.  If  the 
first  coating  does  not  give  an  even  coat,  the  paper  may 
be  floated  again  when  it  is  dry.  The  paper  should  be 
dried  in  the  dark. 

To  sensitize  this  paper  with  the  ethereal  solution, 
the  latter  must  be  made  by  shaking  15  ccm  of  30  per 
cent  peroxide  solution  with  200  ccm  ether  for  about 
ten  minutes  and  allowing  to  settle  in  a  burette  or  funnel; 
the  water  is  then  drawn  off.  This  forms  a  one  per  cent 
solution  of  peroxide  in  ether.  It  must  be  noted  that 
the  peroxide  solution  is  not  the  household  one,  which 
only  contains  three  per  cent  of  peroxide;  the  proper  one 
is  ten  times  the  strength,  and  is  sold  as  "perhydrol." 

If  it  is  considered  preferable  to  use  the  ordinary  per- 
oxide solution,  then  this  must  be  used  instead  of  water 
to  make  the  gelatine  solution,  and  the  temperature  must 
be  kept  as  low  as  possible  in  melting  it.  It  is,  in  fact, 
advisable  to  soak  the  gelatine  for  thirty  minutes  before 
melting.  The  dye  solutions  may  be  added  in  the  same 
way  as  above,  but  probably  the  erythrosin  will  have  to 
be  increased  to  30  to  40  ccm.  This  can  be  determined 
as  before. 

Instead  of  using  the  peroxide  as  sensitizer,  either 
anethol  or  thiosinamin  may  be  substituted.  Anethol 
is  the  camphor  obtained  from  aniseed  oil,  and  has  its 
characteristic  smell.  Thiosinamin  is  a  colorless  crys- 
talline substance  obtained  from  oil  of  mustard,  and  has 
but  a  faint  garlic  odor.  A  saturated  solution  should 
be  made  of  the  former  in  water  and  the  paper  bathed 


THE  BLEACH-OUT  PROCESS  183 

therein,  or  10  drops  of  an  alcoholic  solution  may  be  added 
to  the  gelatine.  In  the  case  of  thiosinamin,  one  per 
cent  may  be  added  to  the  gelatine  just  before  coating. 
In  lieu  of  gelatine,  collodion  may  be  employed,  about 
three  per  cent  of  pyroxylin  in  alcohol-ether  (equal  parts 
of  each).  The  best  method  of  working  is  to  prepare  the 
collodion  as  follows: 

Pyroxylin  30  g 

Ether  500  ccm 

Alcohol  250  ccm 

Pour  the  alcohol  on  the  cotton  and  when  thoroughly 
soaked  add  the  ether,  and  shake  until  dissolved.  The 
dyes  should  then  be  dissolved  in  250  ccm  alcohol  and 
added  to  the  collodion,  and  finally  ten  drops  of  anethol. 
If  the  latter  is  obtained  in  crystals,  then  0.5  g  should 
be  added  to  the  alcoholic  dye  solution,  or  the  same  quan- 
tity of  thiosinamin.  Even  more  satisfactory  results 
are  obtained  with  the  following  dyes,  the  quantities 
being  for  1000  ccm  of  collodion: 

Primrose  1.5    g 

Victoria  blue  0.4    g 

Curcumin  crystals  1.66  g 

Auramin  0.34  g 

Curcumin  is  the  coloring  matter  ob tamed  from  turmeric; 
if  there  is  any  difficulty  in  obtaining  it,  some  powdered 
turmeric  may  be  digested  with  alcohol  for  three  or  four 
days  and  then  filtered;  about  ten  per  cent  should  be 
used.  In  this  case  the  yellow  solution  must  be  added 
cautiously  to  the  other  dyes,  testing  occasionally  on 
white  paper,  so  that  a  neutral  grey  is  obtained. 

If  the  opal  glass  is  to  be  used  and  the  picture  subse- 


184  COLOR  PHOTOGRAPHY 

quently  transferred,  the  glass  should  be  coated  with  a 
0.5  per  cent  solution  of  rubber  in  benzol;  ordinary  bi- 
cycle-tire cement  may  be  used,  thinned  down  to  about 
one  per  cent.  The  gelatine  is  coated  on  the  glass  in  the 
usual  way,  and  alter  exposure,  washing,  etc.,  the  edges 
are  cut  round  and  the  paper  squeegeed  down  and  stripped 
when  dry. 

To  improve  the  stability  of  the  dyes  if  anethol  is  used, 
the  prints  should  be  treated  to  successive  baths  of  ben- 
zol, which  dissolves  this.  If  thiosinamin  is  used  they 
must  be  treated  with  a  weak  nitrous  acid  bath,  which 
can  be  made  by  adding  about  10  drops  of  sulphuric 
acid  to  a  five  per  cent  solution  of  sodium  nitrite,  and 
then  washed.  Finally  the  prints  should  be  treated  with 
a  ten  per  cent  solution  of  tannin  followed  by  a  saturated 
solution  of  tartar  emetic  (antimony  potassium  tart- 
rate),  then  rinsed  and  immersed  in  a  saturated  solution 
of  lead  acetate,  washed  and  dried. 

It  is  possible  to  prepare  transparencies  by  this  pro- 
cess, but  as  it  requires  three  or  four  coatings  or  trans- 
fers, the  game  is  not  worth  the  candle,  considering 
that  so  much  better  results  can  be  obtained  by  other 
methods. 


CHAPTER  XIV 

THE  LIPPMANN  PROCESS  OR  INTER- 
FERENCE HELIOCHROMY 

THIS  is  probably  the  most  beautiful  of  all  color  proc- 
esses from  a  theoretical  standpoint  and  yet  is  also 
that  which  has  been  the  least  practised,  mainly  be- 
cause one  has  to  prepare  the  plates,  exposures  are  very 
long,  and  there  is  no  known  means  of  reproducing  the 
results.  It  has  remained,  therefore,  purely  a  labora- 
tory process. 

The  first  suggestion  as  to  the  possibility  of  this  proc- 
ess was  made  by  W.  Zenker  in  1868;  it  was  later  sug- 
gested by  Lord  Rayleigh  in  1887,  and  O.  Wiener  in  1890, 
but  it  was  not  until  1891  that  G.  Lippmann,  of  Paris, 
actually  succeeded  in  obtaining  a  color  photograph 
in  this  way. 

In  order  that  the  subject  may  be  fully  grasped  we 
must  enter,  even  though  but  superficially,  into  an  ex- 
planation of  the  rudimentary  principles  of  light.  A  brief 
explanation  has  already  been  given  of  the  dispersion 
of  light  and  the  occurrence  of  the  Fraunhofer  lines,  and 
the  following  table  gives  the  principal  of  these  in  the 
visible  spectrum  with  their  wave-lengths  and  the  number 
of  vibrations  per  second: 

Fraunhofer  Line      Wave-length    Vibrations  per  Second 

in  Billions 

A  7593-97  395 

B"  6867.38  437 

185 


i86  COLOR  PHOTOGRAPHY 

Fraunhofer  Line     Wave-length  Vibrations  per  Second 

in  Billions 

C  6562.96  457 

Di  5896.08  509 

D2  589°-I3  5°9 

E  527o-43  569 

bi  5183.73  579 

F  4861.43  617 

G  43OI-43  696 

h  4101.84  731 

H  3968.61  760 

K  3933-86  763 

The  wave-lengths  are  given  in  Angstrom  units  (10- 
millionths  of  a  millimeter.) 

Beyond  A  lies  the  infra  red,  the  invisible  region  of 
which  we  are  sensible  in  the  form  of  heat;  while  beyond 
K  is  the  ultra-violet,  by  which  the  chief  chemical  actions 
are  caused. 

Light  always  proceeds  in  straight  lines  and  is  usually 
supposed  to  be  a  wave-like  motion  in  a  hypothetical 
medium  which  is  called  the  ether.  We  may  assume 
that  the  particles  of  the  ether  are  so  closely  compacted 
that  a  disturbance  or  vibration  of  one  must  give  rise 
to  corresponding  vibrations  in  neighboring  particles. 
This  being  granted,  there  must  be  a  certain  time  re- 
quired for  the  transfer  of  the  agitation  from  one  par- 
ticle to  another.  If  we  picture  the  ether  particles  as 
a  series  of  beads  closely  strung  together  on  a  wire, 
we  may  crudely  represent  them  by  I  in  Fig.  21.  If  now 
a  pull  is  given  to  the  first  particle  at  A  the  vibration  will 
travel  along  the  wire  and  the  beads  will  vibrate  to  and 
fro  on  both  sides  of  the  plane  AB  and  we  may,  assuming 


THE  LIPPMANN  PROCESS 


187 


that  the  direction  of  the  light  is  from  left  to  right,  rep- 
resent what  happens  by  //  in  Fig.  21,  in  which  A'B' 
is  the  plane  of  equilibrium  or  rest,  and  a  is  the  crest, 
b  the  trough  of  the  wave;  the  distance  of  the  particles 
a,  b,  c,  from  A'B'  is  called  the  amplitude  of  the  wave. 

A'    '    '  3- 


FIG.  21 

A  wave-length  is  the  distance  between  any  two  points 
similarly  situated  as  regards  the  equilibrium  plane,  so 
that  A  'D',  C'B',  or  ac  are  each  a  complete  wave-length, 
and  obviously  the  midway  points  are  half  wave-lengths, 
thus  A'C  is  the  half  wave-length  of  A'D'. 

When  a  ray  of  light  meets  a  reflecting  surface  it  is 
thrown  off  according  to  a  well-known  law,  that  the 
angle  of  reflection  is  equal  to  the  angle  of  incidence; 
and  if  a  ray  is  incident  normally  to  a  surface,  that  is, 
at  right  angles  to  it,  it  is  reflected  back  at  the  same  angle 
and  on  the  same  path.  We  can  thus  represent  the  state 
of  affairs  by  ///  in  Fig.  21,  and  the  incoming  and 


i88  COLOR  PHOTOGRAPHY 

outgoing  waves  would  travel  the  same  paths;  but  at  the 
points  abed,  which  are  obviously  each  half  a  wave- 
length apart,  the  pull  on  the  ether  particles  would  be  in 
contrary  directions,  as  shown  by  the  arrows;  there- 
fore, as  the  forces  are  equal  it  is  obvious  that  there  is 
no  movement  and  there  can  be  no  light,  consequently  no 
chemical  action.  The  points  abed  are  called  the  "nodes" 
and  the  spaces  in  between  the  "loops,"  in  which  the 
ether  particles  may  be  considered  to  vibrate  to  and  fro 
pendulum  fashion.  Such  a  system  forms  a  series  of 
"stationary"  or  "standing"  waves,  and  it  is  clear  that 
if  such  a  system  traverses  a  sensitive  film,  there  would 
be,  under  proper  conditions,  chemical  action  only  in 
the  loops,  and  on  development  the  metallic  silver  would 
be  deposited  at  these  places  only.  So,  a  series  of  laminae 
would  be  formed  exactly  half  a  wave-length  apart,  their 
distance  of  separation  being  dependent  on  the  color  of 
the  incident  light,  as  will  be  seen  from  the  above  table. 

White  light  incident  on  such  a  laminary  series  of 
mirrors  is  reflected  according  to  its  wave-length;  each 
zone  reflecting  only  light  of  that  color  which  has  a  wave- 
length corresponding  to  twice  the  distance  of  separation 
of  the  layers. 

The  fundamental  basis  of  this  process  is  that  the 
sensitive  film  shall  be  transparent  and  in  contact,  during 
exposure,  with  a  reflecting  surface  which  returns  the  light 
on  its  incident  path.  For  the  reflecting  surface,  which 
must  be  in  optical  contact  with  the  film,  Lippmann 
chose  mercury,  which,  as  everyone  knows,  is  liquid  at 
ordinary  temperatures  and  highly  reflecting. 

There  are  two  methods  by  which  we  can  prepare  the 
sensitive  film,  either  by  the  old  Taupenot  albumen 
process,  which  was  first  used  by  Lippmann,  or  by  the 


THE  LIPPMANN  PROCESS  189 

gelatine  emulsion   method.     This  latter  is  faster  but 

a  little  more  trouble  to  make.     For  the  albumen  take: 

Albumen  1000  ccm 

Potassium  bromide,  10  %  solution     43  ccm 

Ammonia  43  ccm 

Beat  to  a  froth  and  allow  to  stand  for  twenty-four  hours  to 
liquefy,  and  then  filter  through  glass  wool  or  decant  from 
the  flocculent  sediment.  Glass  plates  should  be  thor- 
oughly scoured  with  hot  soda  and  water,  well  washed 
and  dried,  and  polished  with  alcohol  until  they  show 
a  perfectly  even  film  when  breathed  on.  Ordinary  glass 
is  not  as  a  rule  thick  enough,  and  it  is  more  satisfactory 
to  use  white  plate  glass,  about  one  sixteenth  inch  thick. 
As  the  film  is  extremely  transparent  and  it  is  not  easy 
to  tell  which  side  has  been  coated,  it  is  as  well  to  mark 
the  wrong  side  with  a  diamond  or  the  edge  of  a  three- 
cornered  file.  It  will  also  be  found  that  as  a  rule  one 
side  of  the  glass  is  smoother  than  the  other,  and  this 
smooth  side  should  be  coated;  it  is  easy  to  detect  the 
smoother  side  by  holding  the  glass  level  with  the  eyes  and 
glancing  along  it. 

The  albumen  is  the  white  of  eggs,  and  if  the  operator 
is  not  accustomed  to  separating  the  whites  from  the 
yolks,  it  is  as  well  to  break  each  egg  separately  into  a  cup 
and  then  strain  off  the  white  into  the  bulk.  The  whipped 
and  filtered  albumen  will  keep  for  two  or  three  months 
in  a  well-corked  bottle. 

The  glass  should  be  flowed  over  with  this  solution, 
drained  for  about  thirty  seconds  and  then  placed  on  a 
leveled  slab  to  dry  in  a  place  free  from  dust.  The  plates 
should  then  be  heated  for  two  minutes  to  60°  C.  (140°  F.) 
and  allowed  to  cool.  This  heating  may  be  effected  by 


i9o  COLOR  PHOTOGRAPHY 

placing  the  plates  on  two  or  three  thicknesses  of  blotting 
paper  on  top  of  an  iron  plate,  or  what  is  more  conven- 
ient, an  empty  cracker  tin  of  fair  size.  The  plates  may 
be  placed  in  a  rack  and  with  an  ordinary  Sunsen  burner 
the  temperature  will  soon  be  raised  inside  the  tin,  if  the 
lid  be  put  on.  A  thermometer  can  be  inserted  through 
a  hole  close  to  the  plates.  About  four  minutes  of  this 
treatment  will  suffice.  This  is  less  likely  to  crack  the 
glass.  A  stock  of  plates  can  be  prepared  and  packed  face 
to  face,  wrapped  in  pairs  in  tissue  paper,  and  will  keep 
indefinitely  in  a  dry  place. 
To  sensitize  them,  the  plates  should  be  immersed  in: 

Silver  nitrate  100  g 

Glacial  acetic  acid  100  ccm 

Distilled  water  to  1000  ccm 

This  may  be  used  in  a  dish,  preferably  of  glass.  If  por- 
celain be  used,  a  new  tray  should  be  taken  into  service 
to  avoid  any  possible  contamination  from  previously 
absorbed  solutions.  About  three  minutes  immersion 
is  sufficient.  They  should  then  be  drained  for  about 
one  minute  and  immersed  in  distilled  water  for  five 
minutes,  the  water  poured  off  and  fresh  applied,  and  this 
repeated  six  times.  They  may  then  be  color-sensitized, 
and  although  their  sensitiveness  is  very  low  only  a  green 
light  should  be  used.  The  sensitizer  may  be: 

Glycin  red,  i  :  500  alcoholic  solution  8  ccm 

Cyanin,  i  :  500  alcoholic  solution  2  ccm 

Ammonia,  2  %  solution  15  ccm 

Distilled  water  to  1000  ccm 

Bathe  for  two  minutes,  rinse  in  distilled  water  once, 
and  dry  at  60°  C.  (140°  F.). 


THE  LIPPMANN  PROCESS  19 1 

Valenta  in  1892  was  the  first  to  publish  a  gelatine 
emulsion  formula,  and  various  modifications  have  been 
given;  the  following,  one  of  the  simplest  and  best,  was 
later  also  given  by  Valenta: 

A.  Gelatine  10  g 
Silver  nitrate  6  g 
Distilled  water  300  ccm 

B.  Gelatine  20  g 
Potassium  bromide  2.4  g 
Sodium  chloride,  pure  1.5  g 
Distilled  water  300  ccm 

Soak  the  gelatine  in  water  for  half  an  hour,  then  melt 
by  the  aid  of  a  water  bath  heated  to  40  °  C.  (104  °  F.). 
When  complete  solution  is  obtained,  add  the  salts  and 
cool  the  solutions  to  35  °  C.  (95  °  F.).  Then  pour  A  into 
B  rather  slowly,  stirring  all  the  time,  and  immediately 
pour  into  1000  ccm  of  alcohol  with  constant  stirring. 
The  emulsion  separates  out  into  flocks;  these  should  be 
collected  on  a  piece  of  clean  linen  (an  old  handkerchief 
is  excellent),  the  ends  brought  together  so  as  to  form  a 
bag,  tied,  and  hung  over  a  stick  across  a  beaker  filled 
with  water.  This  should  be  changed  every  five  minutes 
for  half  an  hour.  The  author  has  found  a  slight  modi- 
fication of  this  more  convenient:  a  good  sized  glass  funnel 
to  hold  about  2  liters  is  obtained  and  a  short  piece 
of  rubber  tubing  furnished  with  a  pinchcock  attached 
to  its  stem.  A  piece  of  cloth  large  enough  to  completely 
cover  the  top  of  the  funnel  and  lap  well  over  the  sides 
is  used.  The  emulsion  is  collected  in  this  from  the  al- 
cohol bath  and  it  is  then  gathered  into  a  bag  and  swung 
round  at  arm's  length  for  a  minute  or  two,  which  gets 
rid  of  most  of  the  alcohol.  The  cloth  is  then  stretched 


i9 2  COLOR  PHOTOGRAPHY 

over  the  funnel  and  the  center  pushed  down,  the  funnel 
filled  with  water  and  the  emulsion  stirred  up  with  a  glass 
rod  for  two  minutes  and  then  allowed  to  soak  for  five. 
Then  the  pinch  cock  is  opened,  the  water  run  out,  and  the 
funnel  filled  up  again  so  as  to  completely  cover  the  shreds. 
About  six  changes  of  water  will  thus  wash  it  perfectly. 
Finally  the  ends  of  the  cloth  are  again  gathered  together 
and  the  bag  swung  round  three  or  four  tunes.  The 
emulsion  should  now  be  put  into  a  marked  beaker,  and 
melted  in  a  water  bath,  the  temperature  of  the  emulsion 
not  being  allowed  to  rise  over  35  °  C.  (95  °  F.),  and  the 
volume  made  up  to  600  ccm. 

An  alternative  method  is  to  make  the  emulsion  as 
described  above,  coat  the  plates  immediately  after  fil- 
tering through  the  wool,  place  the  plates  on  a  level 
slab  to  set  and  then  wash  in  running  water  for  fifteen 
minutes,  and  dry. 

These  emulsions  are,  like  all  others,  wanting  hi  color 
sensitiveness.  The  original  plan  of  sensitizing  them  was 
to  bathe  the  coated  plates  in  dye  solutions  and  it  is  still 
the  best  plan,  but  it  may  be  more  convenient,  particu- 
larly if  the  emulsion  is  not  washed  until  after  coating, 
to  add  the  dye  to  the  emulsion.  Both  methods  will  be 
described,  but  we  must  deal  with  the  coating  first.  It 
was  originally  supposed  that  a  very  thin  film  of  emulsion 
was  necessary,  and  the  plates  were  coated  and  then 
whirled  to  sling  off  all  but  a  very  thin  film.  It  has  now 
been  discovered  that  such  thin  coats,  while  they  are 
rather  faster,  are  not  essential.  The  easiest  plan  in  coat- 
ing is  to  place  the  plates  in  a  stack  against  the  wall  or 
other  convenient  place,  pick  up  the  first  with  a  pneu- 
matic bulb,  pour  over  the  emulsion  to  freely  cover  the 
surface,  drain  for  fifteen  seconds,  and  then  place  on  a 


THE  LIPPMANN  PROCESS  193 

level  slab  to  set.  Practically,  the  thinner  the  coat  the 
faster  the  plate,  and  if  the  above  method  gives  too  slow 
a  plate,  then  the  glass  may  be  warmed,  which  will  cause 
more  emulsion  to  drain  off. 

All  the  original  formulas  for  color-sensitizing  called  for 
the  old  cyanin,  but  much  better  results  can  be  obtained 
with  the  newer  isocyanins,  and  pinachrom  is  very  satis- 
factory. For  the  bath  method  use: 

Pinachrom,  i  :  1000  alcoholic  solution        5  ccm 
Distilled  water  to  1000  ccm 

Borax,  saturated  solution  10  ccm 

Bathe  four  minutes,  rinse,  and  dry  rapidly.  As  full  de- 
tails have  already  been  given  as  to  bathing  and  drying 
plates  there  is  no  need  to  add  more.  Green  light  must 
be  used  as  soon  as  the  dye  is  added,  but  before  that 
a  bright  orange  light  may  be  used.  If  it  is  thought  that 
sufficient  red  sensitiveness  is  not  obtained  with  the  above 
dye,  though  this  will  only  be  noticed  in  spectrophotog- 
raphy,  then  a  mixture  of  sensitol  green  and  sensitol  vio- 
let may  be  used,  in  the  ratio  of  two  parts  of  the  former 
to  one  of  the  latter;  and  not  more  than  6  ccm  should 
be  added  to  the  bath.  If  the  dye  is  to  be  added  to  the 
emulsion,  then  3  ccm  of  the  dye  solutions  should  be  added 
to  looo  ccm  of  emulsion. 

Before  leaving  the  emulsion  making  it  may  be  useful 
to  point  out  that  H.  E.  Ives  has  stated  that  the  best 
results  are  obtained  in  spectrum  work,  for  which  the 
process  is  eminently  suited,  by  using  the  following 
solutions: 

A.  Gelatine  20  g 

Distilled  water  500  ccm 


I94  COLOR  PHOTOGRAPHY 

B.  Gelatine  40  g 
Potassium  bromide  5  g 
Distilled  water  1000  ccm 

C.  Silver  nitrate  6  g 
Distilled  water  100  ccm 

Dissolve  the  gelatine,  cool,  add  the  salts,  then  add  A 
to  C  and  pour  into  B.  Working  temperature  35  °  C. 
(95  °  F.).  Coat  the  plates  by  flowing  the  emulsion  on 
to  cold  glass,  drain  off  and  set,  and  wash  the  plates  for 
fifteen  minutes.  The  emulsion  should  be  color-sensi- 
tized by  adding  i  ccm  of  the  dye  solution  to  100  ccm, 
or  for  bathing  the  strength  should  be  i  :  100,000. 

As  previously  stated,  the  film  is  exposed  in  contact 
with  mercury,  and  obviously  the  glass  must  face  toward 
the  lens.  The  chief  difficulty  here  is  the  plate-holder; 
it  must  be  capable  of  holding  the  mercury  without  leak- 
age, and  the  mercury  must  be  run  in  and  out  when  the 
plate  is  in  position.  Specially  constructed  holders  are 
obtainable  commercially  and  it  will  be  better  to  pur- 
chase one;  but  the  following  brief  description  may  be 
useful.  The  front  of  the  holder  carries  a  strip  of  rubber 
about  4  mm  wide  and  2  mm  thick,  against  which  the 
glass  is  pressed.  The  back  is  a  solid  piece  of  wood, 
metal  lined,  with  a  rubber  strip  all  round,  and  this  is  a 
firm  but  resilient  red  rubber.  The  back  fits  tightly  in 
place  and  is  held  by  two  steel  cross  bars  that  fit  on  pins 
with  fly  nuts  which  screw  it  firmly  into  place.  In  one 
corner  of  the  back  is  screwed  a  small  steel  pipe  to  which 
is  fastened  a  rubber  tube,  connected  with  the  mercury 
reservoir;  at  the  diagonally  opposite  top  corner  is  a 
screw,  with  a  hole  driven  right  through  its  length  and 
a  small  cap  fitted;  the  purpose  of  this  is  to  allow  egress 


THE  LIPPMANN  PROCESS  195 

of  the  air  as  the  mercury  flows  in.  The  lower  pipe  is 
fitted  with  a  tap;  to  fill  the  slide  with  mercury,  the  tap 
is  opened,  the  screw  cap  unloosened  and  the  container 
slowly  and  gradually  raised  until  it  is  higher  than  the  top 
of  the  holder;  the  tap  is  then  turned  off  and  the  container 
can  be  laid  on  the  back  of  the  camera.  After  exposure, 
the  tap  is  opened,  the  container  slowly  lowered,  and  the 
mercury  runs  back.  This  holder  and  the  mercury  make 
the  whole  very  heavy  and  allowance  must  be  made  for 
this. 

It  is  very  important  that  the  mercury  be  kept  clean, 
and  if  pure  in  the  first  place  it  can  be  used  repeatedly 
without  trouble.  The  best  way  to  clean  it  is  to  procure 
a  large  chamois  leather;  well  wash  this  in  warm  water 
and  soap,  and  dry;  then  soak  in  gasoline  for  an 
hour  or  two,  kneading  it  occasionally  with  the  hands, 
and  dry.  This  may  make  the  leather  harsh  and  stiff, 
but  it  can  be  easily  suppled  by  pulling  and  working  be- 
tween the  hands.  It  should  be  placed  in  a  clean  dish  and 
the  mercury  poured  into  the  middle  and  run  backwards 
and  forwards  for  a  short  time,  and  then  the  ends  of  the 
leather  gathered  together  and  twisted  round  so  as  to 
force  the  mercury  through. 

One  caution  is  necessary;  immediately  after  exposure 
the  mercury  must  be  run  out;  if  left  in  contact  with  the 
film,  the  latent  image  on  this  is  completely  destroyed. 

It  is  impossible  to  give  a  very  definite  idea  of  exposure, 
but  the  plates  are  from  1000  to  2000  times  slower  than  a 
fast  plate.  For  a  landscape  in  bright  sunlight,  with  a 
lens  working  at  / :  4.5,  the  exposure  will  be  from  one 
to  two  minutes.  It  will  be  seen  that  portraiture  by  this 
process  is  almost  impossible,  though  Professor  Lippmann 
did  succeed  in  taking  some  very  good  portraits.  For 


196  COLOR  PHOTOGRAPHY 

still  life  the  plates  are  excellent.  For  spectrographic 
work,  with  a  slit  width  of  0.3  mm,  a  condenser  and  sun- 
light, the  exposure  will  be  about  one  minute. 

For  development  pyro-ammonia  has  been  the  fa- 
vorite, and  the  following  is  a  typical  formula: 

A.  Pyrogallol  i  g 
Distilled  water  100  ccm 

B.  Potassium  bromide  20  g 
Ammonia,  sp.  gr.  0.96  67  ccm 
Distilled  water  100  ccm 

For  use,  mix  10  parts  A,  20  parts  B,  and  140  parts  water. 
Duration  of  action  about  three  minutes,  and  the  plate 
should  be  at  once  well  washed. 

There  has  been  considerable  discussion  as  to  whether 
these  pictures  should  be  fixed  or  not;  for  the  most  correct 
rendering  of  color  they  should  not  be,  and  this  is  par- 
ticularly applicable  to  spectrum  work.  If  they  are  fixed 
the  distance  of  separation  of  the  silver  laminae  is  slightly 
reduced  and  consequently  there  is  a  slight  change  of 
color.  For  ordinary  work,  the  best  fixer  is  a  five  per  cent 
solution  of  potassium  cyanide,  which  should  not  be  al- 
lowed to  act  longer  than  ten  to  fifteen  seconds;  then  the 
plates  should  be  rapidly  washed  under  a  tap  for  about 
ten  minutes  and  dried. 

An  alternative  process  and  one  which  has  much  to 
recommend  it,  is  development  with  the  following  hydro- 
chinon  developer: 

Hydrochinon  3  g 

Sodium  sulphite,  dry  7.5  g 

Potassium  carbonate  2  g 

Potassium  bromide  i  g 

Water  to  100  ccm 


THE  LIPPMANN  PROCESS  197 

After  washing  for  ten  minutes,  the  plate  should  be 
immersed  in  a  one  per  cent  solution  of  mercuric 
chloride  and  dried.  This  gives  the  most  brilliant 
colors. 

The  colors  are  only  seen  when  the  pictures  are  ex- 
amined at  a  certain  angle,  and  then  are  very  pale,  due 
to  the  reflection  of  white  light  from  the  surface  of  the 
film.  To  destroy  this  a  glass  prism  of  low  angle,  10  to 
12  degrees,  is  cemented  to  the  surface  with  Canada  bal- 
sam. These  prisms  can  be  obtained  from  any  opti- 


C  FIG.  22  D 

cal  house  at  a  reasonable  price,  as  accuracy  of  surface 
and  angle  are  not  important.  The  Canada  balsam  used 
must  be  diluted  with  benzol  or  xylol,  not  chloroform, 
as  the  latter  in  time  bleaches  the  image.  Before  sealing 
with  the  prism,  a  very  pretty  experiment  can  be  per- 
formed. Examine  the  picture  at  the  best  angle,  and  it 
is  better  to  support  it  in  one  position  and  shift  your 
position  until  this  is  attained.  Then,  with  a  glass  tube, 
blow  on  the  film  and  the  colors  will  be  seen  to  change 
as  the  gelatine  between  the  laminae  swells.  All  colors 
become  more  red,  while  as  the  moisture  dries  out  they 


198  COLOR  PHOTOGRAPHY 

change  back  to  blue.  It  is  thus  possible  to  slightly  alter 
the  colors  of  a  heliochrome,  either  by  warming  or  damp- 
ing, and  as  soon  as  the  correct  colors  are  seen  it  should 
be  cemented  up.  The  prism  should  be  clipped  on  to 
the  picture  and  then  it  should  be  placed  in  a  warm  place 
to  dry.  When  dry,  the  excess  balsam  should  be  scraped 
off,  the  edges  bound  up  with  black  paper,  and  the  back 
of  the  glass  bearing  the  picture  painted  with  black 
varnish. 
These  pictures  are  best  seen  when  side  light  is  pre- 


FIG.  23 


vented  from  reaching  their  surfaces,  and  a  viewing  box  can 
easily  be  made  as  shown  in  Fig.  22.  In  this  ABCD  is 
the  box,  in  one  end  of  which  is  supported  the  heliochrome, 
while  at  the  other  end  is  a  peep  hole  E  through  which 
the  picture  can  be  seen.  M  is  a  small  piece  of  mirror, 
adjustable  on  a  hinge,  which  throws  the  light  through 
the  aperture  KL  cut  in  the  top  of  the  box.  For  exhibition 
on  a  screen  with  a  lantern,  the  principle  of  the  aphen- 
gescope  or  opaque  object  lantern  projector  must  be  used, 


THE  LIPPMANN  PROCESS  199 

as  shown  in  Fig.  23,  in  which  A  represents  the  arc,  C  the 
condensers,  and  A'  the  image  of  the  arc.  The  helio- 
chrome  is  placed  in  the  plane  HE',  so  that  the  beam  of 
light  just  covers  the  picture,  and  L  is  the  projection  lens, 
which  should  be  placed  as  far  from  HE'  as  this  is  from 
the  point  A',  so  that  the  image  of  the  arc  falls  in  the 
objective;  the  picture  will  then  be  shown  on  the 
screen  SS'. 


CHAPTER  XV 

THE  SEEBECK  PROCESS  OR 

PHOTOGRAPHY  WITH  SILVER 

SUBCHLORIDE 

THIS  is  another  interesting  laboratory  process  of  no 
practical  value  as,  so  far,  no  means  of  fixing  the 
images  has  been  discovered.  It  is  named  after  J.  T.  See- 
beck,  who,  prior  to  1810,  sent  to  the  poet  Goethe  a  treatise 
on  the  action  of  light  on  silver  chloride,  in  which  he  dis- 
closed the  fact  that  under  the  influence  of  the  spectral  rays 
it  assumed  the  colors  incident  upon  it.  Sir  John  Her- 
schel  in  1840,  Robert  Hunt,  J.  W.  Draper  and  others 
followed  on  the  same  lines.  Later,  E.  Becquerel  of  Paris 
paid  particular  attention  to  the  subject  and  so  far  modi- 
fied the  methods  of  the  prior  workers  as  to  use  copper 
plates  silvered  on  their  surface.  The  plate  was  protected 
on  the  back  with  varnish  to  protect  the  copper  base, 
and  was  hung  by  wires  in  a  one  to  eight  solution  of  hy- 
drochloric acid  and  connected  with  a  two-cell  bichro- 
mate battery,  the  opposite  pole  being  a  platinum  plate. 
The  acid  was  electrolytically  decomposed,  the  chlo- 
rine attacking  the  silver  and  forming  silver  chloride. 
The  action  was  so  regulated  that  a  definite  amount  of 
chloride  was  formed,  and  the  plate  was  then  dried  and 
heated  until  the  originally  white  silver  chloride  turned  to 
a  delicate  rose  color.  On  exposure  to  the  spectrum,  or 
colored  light,  it  assumed  the  colors  more  or  less  correctly. 
Becquerel  was  followed  by  Niepce  de  St.  Victor,  who 


THE  SEEBECK  PROCESS  201 

also  used  silvered  plates,  and  A.  L.  Poitevin,  who  did  not 
publish  the  first  account  of  his  work  with  paper  as  the  sup- 
port until  1865,  though  it  was  begun  in  the  early  50*3. 
The  chloride  was  produced  by  alternate  baths  of  salt, 
and  silver  nitrate  and  salt,  as  for  the  success  of  the 
process  an  excess  of  silver  nitrate  must  not  be  present. 
To  accelerate  the  action,  the  paper  was  treated  with  an 
alkaline  bichromate  and  cupric  sulphate,  which  were 
used  with  the  idea  of  absorbing  the  chlorine  set  free 
by  the  action  of  light.  Practically  this  process  is  the 
basis  of  ah1  subsequent  processes. 

Wharton  Simpson,  in  1866,  published  a  method  in 
which  collodio-chloride  of  silver  emulsion  was  coated 
on  glass,  exposed  to  light  until  it  turned  slate  color, 
then  under  the  colored  original.  To  those  desirous  of 
making  their  own  paper  on  the  above  lines,  the  follow- 
ing directions  may  be  useful.  Dissolve  20  g  of  silver 
nitrate  in  12  ccm  distilled  water  by  the  aid  of  heat,  and 
add  to  250  ccm  of  96%  alcohol;  then  add  10  g  of  pyrox- 
ylin, and  then  250  ccm  of  ether.  Also  add  10  g  of  py- 
roxylin to  250  ccm  of  alcohol,  dissolve  in  this  8  g  of  crys- 
tallized strontium  chloride,  and  add  250  ccm  of  ether. 
Pour  the  second  solution  into  the  first  in  small  quanti- 
ties, shaking  after  each  addition.  Allow  to  stand  twenty- 
four  hours,  and  it  is  fit  to  use.  After  coating  the  paper 
or  glass  it  should  be  dried  in  front  of  a  fire. 

Any  chloride  may  be  used  instead  of  the  above  in 
equivalent  weights,  for  instance,  4.3  g  of  potassium, 
5.8  g  of  sodium,  6.3  g  of  ammonium,  6.1  g  of  calcium  or 
7.0  g  of  magnesium  chloride;  all  being  the  anhydrous 
salts. 

It  is  not,  however,  such  an  easy  matter  for  the  novice 
to  coat  collodion  on  paper,  and  any  commercial  print- 


202  COLOR  PHOTOGRAPHY 

ing-out  paper  may  be  used,  if  treated  according  to  the 
following  method,  which  was  patented  by  Kopp  in  1891, 
although  it  is  practically  Poitevin's  1866  process.  Im- 
merse the  paper  in  a  5  per  cent  solution  of  salt  for  fif- 
teen minutes.  The  purpose  of  this  is  to  convert  into 
silver  chloride  the  excess  of  silver  nitrate  and  organic 
salt,  usually  citrate  or  tartrate,  that  are  always  present 
in  these  papers.  Then  hang  up  to  dry,  and  in  this  con- 
dition it  will  keep  for  a  long  time  in  the  dark.  Then  in 
a  clean  dish  immerse  in  the  following: 

Zinc  chloride  i  g 

Sulphuric  acid  12  drops 

Distilled  water  1000  ccm 

Expose  to  diffused  daylight  until  the  paper  turns 
bluish-green,  taking  care  that  the  surface  of  the  paper 
is  always  beneath  the  solution,  and  that  the  bluish- 
green  color  is  not  overstepped.  After  this  the  paper 
should  be  well  washed,  dried  off  between  blotting  papers, 
and  dried  in  the  dark.  In  this  condition  it  will  keep 
for  a  long  time.  The  following  solution  is  then  prepared: 

Potassium  bichromate  150  g 

Cupric  sulphate  150  g 

Distilled  water  to  1000  ccm 

Heat  until  this  boils,  and  then  add: 

Mercuric  nitrate  150  g 

Nitric  acid  5  ccm 

Distilled  water  q.  s. 

The  nitrate  should  be  placed  in  a  porcelain  evaporating 
dish,  the  acid  added,  and  then  distilled  water  in  small 
quantities,  heat  being  applied  and  more  water  added 


THE  SEEBECK  PROCESS  203 

in  small  quantities  until  solution  is  effected.  This  should 
then  be  added  to  the  boiling  copper  solution  with  con- 
stant stirring.  A  reddish  precipitate  will  be  formed, 
and  the  solution  should  then  be  allowed  to  cool  and  fil- 
tered, and  either  water  added  or  the  solution  evaporated 
till  it  measures  1000  con.  This  will  keep  well  in  the  dark 
in  a  stoppered  bottle.  The  blue-green  paper  should  be 
immersed  in  this  solution  for  thirty  seconds,  or  until 
it  becomes  colorless,  well  drained  and  then  immersed  in 
a  3  per  cent  solution  of  zinc  chloride  and  rocked  till  it 
turns  blue  again,  then  well  washed  in  running  water, 
blotted  off,  and  allowed  to  hang  up  for  about  ten  minutes 
and  exposed  while  still  damp.  Yellow  and  green  soon 
make  their  appearance,  and  when  sufficiently  intense; 
the  paper  should  be  removed  and  the  yellow  and  green 
parts  painted  with  a  varnish.  An  ordinary  negative 
varnish  may  be  used,  and  two  or  three  coats  should  be 
given,  the  paper  being  heated  after  each  coat  so  as  to 
thoroughly  dry  it.  The  other  colors  can  be  seen  but 
faintly,  being  covered  with  a  yellow  fog,  and  to  remove 
this  the  print  should  be  immersed  in  a  2  per  cent  solution 
of  sulphuric  acid  and  rocked  until  the  colors  are  visible, 
then  rapidly  washed,  blotted  off  and  dried. 

In  this  condition  all  the  colors,  as  well  as  black  and 
white,  should  be  well  represented,  but  they  are  not  per- 
manent, nor  is  it  possible  to  make  them  completely  so; 
but  they  can  be  made  more  so  by  immersion  for  five  min- 
utes in  the  mercury-bichromate  bath,  in  which  all  color 
disappears,  then  in  the  sulphuric  acid  bath,  which  again 
develops  the  color.  The  print  should  be  thoroughly 
blotted  off  and  painted  with  gum  arabic  acidulated  with 
5  per  cent  sulphuric  acid.  This  can  be  made  by  dissolv- 
ing 20  g  of  gum  in  100  ccm  of  water,  adding  5  ccm  of 


204  COLOR  PHOTOGRAPHY 

strong  sulphuric  acid,  with  constant  stirring,  and  then 
filtering.  This  acts  as  a  provisional  fixer  or  desensitizer 
and  also  brightens  up  the  colors  by  giving  them 
more  gloss. 

Instead  of  the  zinc  chloride  solution,  advised  above, 
a  one  per  cent  solution  of  sodium  nitrite  (not  nitrate) 
may  be  used.  Undoubtedly  the  above  process  is  the  most 
satisfactory  if  correctness  of  coloring  is  considered,  but 
some  fairly  interesting  results  can  be  secured,  with  far 
less  trouble,  by  treating  commercial  printing-out  paper 
with  the  salt  or  zinc  chloride  solutions  to  insolubilize  the 
excess  of  silver,  then  merely  exposing  to  light  until  it 
turns  violet  or  slaty  blue,  and  exposing  under  the  colored 
original.  This  does  not  however,  give  whites  or  blacks, 
and  better  results  are  obtained  by  exposing  under  the 
nitrite  first. 

The  results  obtained  by  Kopp's  method  may  be  ex- 
amined by  weak  daylight,  and  they  will  keep  in  the 
dark  unchanged  for  years;  some  have  been  kept  for 
twenty  years. 


CHAPTER  XVI 
THE  DIFFRACTION  PROCESS 

THIS  process  was  invented  by  Professor  R.  W.  Wood, 
of  Johns  Hopkins  University,  and  is  a  beautiful 
application  of  the  phenomena  of  diffraction  by  gratings. 
It  is,  however,  merely  a  laboratory  process,  as  the  results 
are  only  capable  of  being  seen  by  one  person  at  a  time 
or  of  being  projected  on  a  very  limited  scale,  nor,  so  far 
as  the  author  is  aware,  are  the  necessary  diffraction 
gratings  commercially  available.  On  the  other  hand, 
it  is  a  comparatively  easy  process  and  capable  of  indefi- 
nite reproduction. 

The  theory  involved  is  simple,  and  no  explanation 
will  be  required  for  those  familiar  with  the  phenomena 
of  gratings.  A  grating  is  a  sheet  of  metal  or  glass  ruled 
with  extremely  fine  lines,  ranging  from  2000  to  20,000 
per  inch.  When  white  light  falls  on  a  glass  grating  it 
is  split  up  into  a  series  of  spectra,  as  shown  in  Fig.  24. 


II 

C           lot.                 2nd.               Sttt 

FIG.  24 

The  light  passing  straight  through  the  grating  is  seen 
as  a  white  central  band  C;  on  each  side  are  seen  the  spec- 
tra with  the  violet  end  nearest  the  central  image.  The 
spectra  are  called  the  first,  second,  third,  etc.,  to  the  n\h 
205 


206 


COLOR  PHOTOGRAPHY 


order  spectra,  according  to  their  position  as  regards  the 
central  beam;  and  these  spectra  become  longer  and 
fainter  the  higher  their  order.  Theoretically  there  is  no 
limit  to  the  number  of  spectra  that  can  thus  be  formed, 
but  the  first  order  spectrum  is  the  only  one  used  in  this 
process,  because  it  is  the  brightest.  The  distance  from 
the  central  beam  depends  entirely  upon  the  number 
of  lines  per  unit  or  inch,  and  the  finer  the  ruling,  that  is, 
the  greater  the  number  of  lines  per  inch,  the  further 
removed  are  the  spectra  from  the  central  image.  It 
is  obvious,  then,  that  we  can  so  choose  the  rulings  that 
any  three  colors  may  be  on  the  same  plane,  as  roughly 
shown  in  Fig.  25,  in  which  the  light  and  the  gratings 


are  supposed  to  be  behind  the  page,  and  we  are  looking 
on  the  spectra  formed  on  the  paper.  With  three  gratings, 
that  which  gives  the  image  A  has  the  coarsest  ruling, 
that  which  gives  B  being  finer,  and  C  being  finer  still. 
If  these  rulings  are  correctly  chosen,  the  red  of  A,  the 
green  of  B,  and  the  blue  of  C  will  all  appear  on  the  same 
vertical  line  OO. 

It  has  already  been  pointed  out  that  from  the  three 
lights  red,  green  and  blue  we  can  produce  all  colors,  so 


THE  DIFFRACTION  PROCESS  207 

obviously  in  this  case  we  are  in  a  position  to  reproduce 
all  colors  by  the  use  of  three  gratings,  either  by  project- 
ing the  spectra  on  one  plane  or  by  superposing  the 
gratings;  and  this  is  the  fundamental  basis  of  the 
diffraction  process.  The  three  gratings  are  printed 
on  one  bichromated  gelatine  film. 

The  rulings  chosen  by  Professor  Wood  had  2000, 
2400  and  2750  lines  per  inch  for  the  red,  green  and  blue 
respectively,  but  one  is  not  tied  to  these  particular  num- 
bers, finer  gratings  being  used  in  the  same  ratio. 

Three  constituent  negatives  are  required,  taken  in 
the  usual  way  through  the  red,  green  and  blue  selective 
filters.  From  these  negatives  three  positives  in  silver 
must  be  made  as  usual;  from  these  positives  the  final 
result  is  obtained.  The  support  for  the  final  picture 
must  be  plate  glass,  as  ordinary  glass  is  not  flat 
enough.  The  sensitive  mixture  is: 

Gelatine  40  g 
Potassium  bichromate,  saturated 

solution  50  ccm 

Distilled  water  1000  ccm 

Soak  the  gelatine  in  the  water  for  fifteen  minutes,  then 
dissolve  by  heat  and  add  the  bichromate  solution,  and 
filter  while  hot.  The  glass  must  be  thoroughly  cleaned 
and  polished.  Enough  of  the  solution  is  poured  on 
to  cover  the  surface,  the  excess  drained  off  for  about 
ten  seconds,  and  then  the  plate  placed  on  a  leveled  slab 
to  set  and  dry  in  the  dark.  The  coating  should  be 
thin  and  the  plates  will  dry  in  about  two  hours. 

There  are  two  methods  of  printing,  by  contact  or 'by 
projection.  Of  the  two  possibly  the  latter  is  the  easier, 
although,  unless  an  arc  lamp  is  available,  the  exposure 


208  COLOR  PHOTOGRAPHY 

is  unduly  prolonged;  with  an  arc  it  is  approximately 
from  one  to  two  minutes.  The  main  difficulty  is  the 
registration  of  the  images,  though  this  may  be  gotten 
over  by  making  ink  dots  on  the  glass  side  of  the  posi- 
tives and  bringing  these  into  register.  It  is  as  well  to 
support  the  two  positives  in  a  clip,  such  as  is  used  for 
holding  lantern  slides  for  binding,  and,  with  the  aid  of  a 
focusing  magnifier,  bring  the  two  images  into  registra- 
tion; then,  with  a  pen,  put  a  dot  of  ink  on  the  glass  of 
the  positive  nearest  the  eye  corresponding  with  some 
clearly  marked  object  at  one  side  of  the  picture,  and 
also  make  another  dot  at  the  top  or  bottom  of  the  posi- 
tive. Then  reverse  the  positives,  putting  that  which 
was  nearest  the  eye  farther  away;  again  make  the  images 
coincide  and  put  on  ink  dots  to  register  with  the  first 
ones;  repeat  this  for  the  third  positive. 

A  lens  must  be  used  to  project  the  image  of  the  posi- 
tive on  the  sensitive  plate.  This  lens  may  be  supported 
in  a  V-shaped  block  of  wood  or  clamped  in  an  ordinary 
retort  clamp,  as  this  latter  enables  one  to  adjust  it  later- 
ally and  horizontally.  Assuming  that  the  positives  are 
to  be  reproduced  the  same  size,  then,  as  is  well  known, 
there  must  be  just  double  the  equivalent  focus  between 
the  lens  and  the  positive  and  the  same  distance  between 
the  lens  and  the  plate.  No  elaborate  means  are  required 
for  holding  the  sensitive  plate,  but  it  must  be  held  rigidly 
hi  the  same  position  for  the  three  exposures.  The  posi- 
tives are  placed  near  the  arc;  it  should  be  possible  to  place 
all  three  in  approximately  identical  positions,  and  this 
can  be  effected  if  they  are  placed  in  a  printing  frame 
and  jammed  down  into  one  corner.  A  sheet  of  yellow 
glass,  or  a  fixed-out  plate  deeply  stained  with  tartrazin, 
must  also  be  provided. 


THE  DIFFRACTION  PROCESS  209 

To  obtain  even  illumination  of  the  positives,  a  con- 
denser is  essential,  and  it  is  obvious  that  a  projection 
lantern  will  considerably  facilitate  matters.  One  of  the 
gratings  is  placed  in  contact  with  the  sensitive  film, 
the  yellow  glass  interposed  between  the  light  and  the 
condenser,  and  the  image  of  the  positive  sharply  fo- 
cused on  the  film;  then  without  disturbing  its  position 
at  all,  the  grating  should  be  removed  and  ink  dots  made 
on  the  film  corresponding  to  the  dots  on  the  positive. 
These  give  one  a  visible  means  of  registering  the  three 
images. 

The  grating  with  the  lowest  number  of  rulings  is  placed 
in  contact  with  the  film,  the  yellow  glass  removed  and 
the  exposure  made  through  the  positive  taken  through 
the  red  filter.  The  yellow  safe-light  must  now  be  placed 
in  front  of  the  light,  the  positive  taken  through  the  green 
filter  substituted  for  the  red  one,  the  next  finer  grating 
placed  in  contact  with  the  film  in  place  of  the  coarser 
one,  the  second  exposure  made,  and  the  operation  re- 
peated for  the  third  picture.  A  preferable  procedure, 
however,  is  to  make  the  third  picture  on  a  separate 
plate,  using  the  finest  grating,  and  turn  the  positive 
around  so  that  the  image  is  reversed,  as  this  can  then 
be  used  as  a  cover  glass  for  the  other  two  pictures.  The 
exposed  plates  are  washed  in  water  at  35  °  C.  (95  °  F.) 
and  then  stood  up  to  dry.  It  should  be  noted  that  the 
ruling  of  the  gratings  should  be  vertical. 

The  results  are  without  any  color  at  all;  but  when 
properly  viewed  the  colors  are  at  once  seen.  The  view- 
ing arrangements  are  very  simple,  being  nothing  more 
than  a  double  convex  lens,  against  which  is  placed  the 
grating-picture,  and  a  metal  disc  with  a  small  peep- 
hole in  the  center  which  is  placed  at  the  focus  of  the 


210  COLOR  PHOTOGRAPHY 

lens.  The  light  should  be  practically  a  line  and  this 
can  easily  be  arranged  by  using  the  edge  of  a  bats-wing 
gas  burner,  or  an  electric  light  may  be  used  with 
an  opaque  screen  with  a  slit  about  one  eighth  inch  wide 
cut  in  it.  If  the  light,  lens  and  peephole  are  all  in  line, 
one  only  sees  the  central  white  image  but  if  the  lens 
and  peephole  be  placed  at  a  slight  angle,  the  colors  in- 
stantly start  into  view.  What  this  angular  arrange- 
ment does,  of  course,  is  to  throw  the  first  order  spectra 
into  the  eye.  Knowing  the  colors  of  the  original,  one 
soon  knows  the  particular  angle  that  will  give  the  correct 
coloring;  but,  as  an  experiment,  the  effect  of  different 
angles  should  be  tried,  for  it  is  possible  in  this  way  to 
show  green  cherries  or  roses  with  red  leaves,  or  blue 
roses  with  purple  leaves. 

In  contact  printing,  the  same  care  must  be  taken 
about  registration,  and  it  can  easily  be  worked  out  in 
the  same  way  by  ink  dots  or  card  guides.  The  exposure 
is  best  made  by  direct  sunlight,  and  the  sensitive  plate 
and  the  grating,  with  the  positive  slide  outside,  should 
be  placed  at  the  bottom  of  a  narrow  lidless  box,  painted 
black  inside,  and  pointed  to  the  sun.  The  exposure  at 
midday  will  be  about  thirty  seconds. 

Having  once  obtained  a  successful  result,  any  number 
can  be  printed  from  it  by  contact  on  bichromated  gela- 
tine. Failure  of  registration  is  shown  by  overlapping  of 
the  edges  of  objects  hi  the  result,  and  errors  in  exposure 
may  be  seen  by  the  colors  being  incorrect.  For  instance, 
overexposure  with  the  red  grating  will  cause  yellows  to 
be  too  orange,  and  errors  in  the  blue  printing  will  make 
the  greens  too  blue.  Modifications  of  this  process  have 
been  suggested,  but  as  they  complicate  without  material 
improvement,  we  can  ignore  them.  T.  Thorp  used  a 


THE  DIFFRACTION  PROCESS  211 

single  grating  and  changed  its  angle  for  each  exposure. 
While  this  gives  as  good  results,  it  necessitates  the  use  of 
three  illuminants  with  three  separate  pictures  inclined 
with  regard  to  the  rulings,  and  the  viewing  apparatus 
is  more  complicated.  H.  E.  Ives  proposed  to  use  a  black 
and  white  line-screen  as  well  as  the  positive,  and  change 
the  angle  of  the  grating  after  each  exposure,  but  this 
necessitates  rather  careful  mechanism  for  changing  the 
angle  and  shifting  the  line-screen  after  each  exposure. 

As  pointed  out,  as  far  as  possible  a  line  of  light  should 
be  used  for  viewing,  for  if  too  broad  a  source  is  used  one 
has  numerous  spectra  superimposed  and  consequent 
lack  of  color,  as  white  is  thus  formed.  If  the  line  of  light 
is  at  right  angles  to  the  ruling  of  the  gratings,  only  a  nar- 
row stripe  of  color  is  seen,  as  the  spectra  are  formed  on 
each  side  of  the  central  beam  parallel  to  it  and  to  the 
direction  of  the  rulings. 


CHAPTER  XVH 
THE  PRISMATIC  DISPERSION  PROCESS 

THIS  process  was  first  suggested  by  Chas.  Cros  in 
1869.  He  proposed  to  split  up  the  light  by  means  of  a 
prism,  which  was  to  be  turned  so  as  to  direct  the  three  col- 
ored rays  to  slightly  different  positions  on  the  sensitive  sur- 
face. Cros'  idea  was  purely  theoretical  and  he  made  no 
attempt  to  carry  the  process  into  practice.  The  idea 
was  subsequently  taken  up  by  J.  Drac  and  L.  Moelants, 
but  has  never  passed  the  experimental  stage.  Subse- 
quently F.  M.  Lanchester,  in  1894,  patented  a  modi- 
fied process  in  which,  instead  of  using  a  single  slit  to  ob- 
tain a  single  spectrum,  which  obviously  considerably 
limited  the  available  light,  a  series  of  slits,  that  is,  a  black 
and  white  line  screen,  was  used,  so  that  a  series  of  minute 
spectra  would  be  formed  on  the  sensitive  surface.  As- 
suming that  the  light  incident  on  these  slits  was  re- 
flected from  a  colored  object,  it  is  clear  that  only  the 
colors  of  the  object  would  appear  in  the  individual  spec- 
tra. Various  modifications  of  this  process  were  proposed 
by  Raymond,  Cheron,  Lippmann  and  others.  The  dis- 
advantages of  all  these  methods  was  that  the  image  of 
the  object  and  that  of  the  slits  must  be  simultaneously 
projected  on  the  sensitive  surface;  consequently  the 
apparatus  was  extremely  bulky,  and  the  available  light 
very  little.  They  also  suffered  from  the  obvious  dis- 
advantage, incident  to  all  prismatic  spectra,  that  the  dis- 
tribution of  the  colors  is  very  unequal,  the  reds  being 


THE  PRISMATIC  DISPERSION  PROCESS     213 

cramped  together  and  the  blues  unduly  spread  out. 
Thus  one  may  roughly  state  that  the  blue  rays  would 
occupy  about  three  times  the  space  of  the  red,  instead 
of  being  proportionately  distributed,  as  in  normal  or 
diffraction  grating  spectra. 

In  1904,  J.  Rheinberg  devised  an  apparatus  in  which 
this  unequal  distribution  of  the  colors  was  overcome 
by  the  use  of  a  speciaUy  computed  direct-vision  prism, 
with  which  the  color  spaces  were  practically  the  same  as 
in  a  normal  spectrum.  This,  like  all  these  processes, 
is  better  fitted  for  the  laboratory  than  for  practical  work, 
as  the  original  taking  apparatus  has  to  be  used  for  view- 
ing the  results.  There  is  no  commercially  available  in- 
strument and  it  would  be  somewhat  costly  to  make. 
Full  details  will  be  found  in  The  Photographic  Journal, 
1912:  162,  and  The  British  Journal  of  Photography, 
1912,  Color  Photography  Supplement,  19,  28,  33,  38. 

Another  process,  which  might  be  called  the  refraction 
process,  was  first  suggested  by  Liesegang  in  1896,  and 
a  year  later  independently  by  J.  A.  C.  Branfill.  In  this 
process  the  action  of  the  cross-lined  screen  is  taken  ad- 
vantage of,  namely  that  each  aperture  in  a  cross-lined 
screen  acts  as  a  pinhole  camera  and  produces  an  image 
of  the  diaphragm.  Thus,  when  using  a  square  diaphragm, 
the  dots  on  the  sensitive  surface  are  square,  and  with 
triangular  stops  three  cornered  figures  are  formed.  If 
the  diaphragm,  instead  of  being  a  single  aperture,  is  di- 
vided into  a  series  of  apertures,  there  are  as  many  dots 
on  the  sensitive  plate  as  there  are  apertures.  This  being 
established,  it  is  clear  that  if  the  stop  aperture  be  split 
up  into  three  areas,  each  covered  by  a  color  filter,  one 
would  have  three  images  formed  in  the  three  colors, 
consequently  the  image  of  a  colored  object  transmitted 


214  COLOR  PHOTOGRAPHY 

by  a  lens  would  be  represented  on  the  sensitive  surface  by 
minute  areas  corresponding  to  the  colors  of  the  subject. 
One  may  look  upon  this  method  as  a  screen-plate  process 
in  which  the  screen-elements  are  optically  formed  during 
exposure  and  not  on  a  separate,  preformed  plate. 

There  is  considerable  loss  of  light  in  this  process,  due 
to  the  fact  that  the  apertures  in  the  cross-lined  screen 
transmit  but  a  fraction  of  the  incident  light.  The  appa- 
ratus necessary  is  only  the  cross-lined  screen,  which  pre- 
sents no  particular  difficulty,  as  it  can  be  obtained  com- 
mercially. The  only  requirements  to  be  satisfied  are 
that  the  opaque  lines  shall  preferably  be  the  same  width 
as  the  transparent  interspaces,  and  that  the  lines  cross 
at  right  angles.  The  fineness  of  the  ruling  is  elastic, 
as  one  may  obviously  decide  to  work  with  a  fairly  coarse 
or  a  fine  ruling,  according  to  the  purpose  of  the  final 
picture.  Probably  for  general  work  from  70  to  100  lines 
per  inch  would  suffice,  as  this  would  give  color  elements 
one-third  the  size,  that  is,  from  210  to  300  per  inch.  Theo- 
retically, there  is  no  limit  to  the  fineness,  but  the  finer  the 
ruling  the  more  difficult  it  becomes  to  register  the  picture. 

The  construction  of  the  diaphragm  is  not  an  easy 
matter,  for  one  is  naturally  limited  as  regards  the  size 
of  the  filters  by  the  working  aperture.  Consequently 
one  must  decide  always  to  use  a  given  aperture  or  else 
to  prepare  as  many  filter  diaphragms  as  may  be  nec- 
essary to  satisfy  the  requirements  of  sharpness  of  the 
image,  taking  into  consideration  here  the  marginal  def- 
inition on  the  plate.  Obviously  the  most  practical 
plan  would  be  to  use  as  large  a  diaphragm  as  possible, 
and,  drawing  a  circle  on  paper  of  the  exact  size,  to  de- 
scribe a  square  outside  the  circle  and  divide  this  into 
equal  areas,  which  shall  be  those  of  the  filters,  trusting 


THE  PRISMATIC  DISPERSION  PROCESS     215 

to  a  supplementary  filter  to  obtain  equal  exposures. 
Or  one  might  vary  the  areas  of  the  filters  corresponding 
to  the  filter  factors,  but  then  one  must  have  unequal 
color  areas  in  the  resultant  picture;  in  all  probability 
this  would  be  the  most  satisfactory  plan,  as  this  will 
theoretically  be  necessary  to  form  a  neutral  grey.  These 
are  points  which  would  have  to  be  worked  out,  as  no  one 
has  done  more,  so  far  as  the  author  is  aware,  than  to 
work  this  process  on  paper. 

The  only  possible  plan  for  making  the  filter  dia- 
phragms would  seem  to  be  to  use  a  microscopic  cover 
glass,  of  the  required  size  to  fit  the  lens  tube,  and  cement 
the  niters  down  in  strip  form,  which  is  not  such  an  easy 
matter,  as  the  edges  must  fit  without  white  interspaces 
or  overlapping.  Or  one  might  expose  on  bichromated 
gelatine  and  stain  up  with  dyes  that  take  differentially 
on  hard  and  unhardened  gelatine;  when  one  would  have 
the  difficulty  of  adjusting  the  color  depth  to  the  rigid 
requirements  of  the  theoretical  filters.  One  also  meets 
here  with  the  difficulty  of  inserting  the  diaphragms  in 
the  lens  tube,  as  it  is  quite  possible  that  a  little  trouble 
might  ensue  in  the  case  of  anastigmats  of  large  aperture 
because  of  the  thickness  of  the  glass,  small  though  this  is. 

It  would  be  necessary  to  use  a  compensating  filter, 
as  in  all  screen-plate  processes,  to  reduce  the  vision  of 
the  plate  to  that  of  the  eye,  and  this  could  only  be  done 
by  trial  and  error,  using  a  white  surface  as  the  object 
and  making  successive  filters  and  exposures  until  it 
was  rendered  as  white. 

There  are  mathematical  rules  for  finding  the  separa- 
tion between  the  cross-lined  screen  and  the  sensitive 
surface,  which  is  dependent  on  the  stop  aperture,  and  the 
extension  of  the  camera;  but  the  simplest  plan  is  to  use 


216  COLOR  PHOTOGRAPHY 

a  magnifier  and  examine  the  image,  and  so  adjust  the 
distance  that  the  colored  rectangles  or  other  figures 
are  seen  to  be  sharply  defined  with  distinct  edges:  this 
involves  a  somewhat  delicate  screw  adjustment  for  the 
screen,  which  must  necessarily  be  at  the  same  distance 
from  the  sensitive  surface  at  all  points.  It  should  be 
mentioned,  in  connection  with  the  focusing,  that  it  is 
impossible  to  obtain  critical  sharpness  with  ground 
glass,  and  assuming  that  the  camera  is  to  be  used  for  other 
work  as  well,  then  the  only  thing  to  do  is  to  mark 
a  small  cross  with  a  hard  lead  pencil  on  the  center  of 
the  ground  glass,  and  cement  a  microscopic  cover  glass 
over  this  with  Canada  balsam.  This  gives  a  per- 
fectly clear  spot  on  which  when  focusing  with  the  naked 
eye  nothing  but  the  cross  can  be  seen;  but,  if  a  magni- 
fier be  used,  the  image  and  the  cross  are  easily  focused. 
The  magnifier  used  should  be  of  the  type  in  which  the 
distance  from  the  glass  can  be  adjusted  and  then  fixed  once 
for  all,  and  it  should  have  a  sleeve  by  which  the  dis- 
tance from  the  glass  is  made  permanent  for  all  time. 
If  the  lead  pencil  cross  be  once  sharply  focused  and  the 
glass  fixed  for  this,  it  must  not  be  again  altered. 

Other  modifications  of  this  process  have  been  sug- 
gested on  paper,  in  which  the  cross-lined  screen  is  elimi- 
nated by  making  the  emulsion  support  act  as  a  series 
of  minute  lenses,  which  should  be  formed  in  a  substance 
like  celluloid,  which  is  plastic  under  heat  and  pressure, 
these  minute  lenses  forming  the  images  of  the  diaphragms 
on  the  posterior  surface  of  the  support,  which  should  be 
covered  by  the  emulsion.  It  would  also  be  possible  to  use 
these  minute  lenticular  forms,  which  can  be  linear, 
cylindrical  or  hexagonal,  on  a  separate  plate  were  it 
possible  to  obtain  contact  with  the  emulsion  surface. 


CHAPTER  XVTH 

TWO-COLOR  PROCESSES,  BI-PACKS  AND 
TRI-PACKS 

THE  possibility  of  using  two  instead  of  three  colors 
was  pointed  out  by  Ducos  du  Hauron  in  1895,  and 
he  suggested  that  red  and  blue  were  quite  sufficient  to 
produce  a  color  result,  provided  that  too  bright  a  light 
was  not  used  for  examination,  or  the  light  was  yellowish, 
or  the  support  was  tinted  yellow.  This  idea  was  fur- 
ther utilized  by  J.  Gurtner,  who,  in  1902,  proposed  to 
use  orange  and  green  as  the  print  ing  colors,  thus  ignoring 
the  deep  reds.  Some  five  years  later  G.  A.  Smith 
adopted  the  red  and  green  dyad  for  the  mixing  of  colored 
lights  for  cinematographic  projection.  That  the  results 
obtainable  by  a  two-color  process  can  never  be  theo- 
retically correct  is  unquestionable;  but  such  pictures, 
when  examined  by  artificial  light,  are  so  satisfactory  as 
to  delude  even  experts.  The  only  colors  that  are  really 
defective  are  the  violets  and  deep  blues,  assuming  red 
and  green  as  the  printing  colors. 

Gurtner's  method  was  to  place  two  sensitive  plates 
in  contact.  The  film  of  the  front  one,  which  was  a 
slow  chloro-bromide  emulsion,  was  stained  orange  and 
turned  with  its  film  towards  the  second  plate,  thus  act- 
ing as  a  filter  for  the  latter.  Ducos  du  Hauron  sug- 
gested a  tri-pack;  that  is  three  sensitive  plates  or  films 
made  up  into  a  block  with  filters  in  between,  so  as  to 
limit  the  action  of  the  spectral  rays.  Obviously,  in  both 
217 


2i 8  COLOR  PHOTOGRAPHY 

cases,  but  one  lens  was  required  and  any  ordinary  camera 
could  be  used  with  slight  alteration  of  the  plate-holders. 
Some  such  process  would  be  invaluable  if  practical,  but 
there  is  a  fly  in  the  ointment. 

It  is  impossible  to  obtain  critical  sharpness  by  any  such 
method.  In  the  first  place,  critical  sharpness  exists  in 
one  plane,  and  one  plane  only;  but,  with  a  comparatively 
small  diaphragm  in  the  lens,  there  is  an  appreciable 
distance  along  the  optical  axis,  through  which  the  sen- 
sitive plate  may  be  moved  without  apparent  loss  of 
sharpness.  But  this  is-  not  sufficient  to  allow  of  three 
plates  or  films  being  used  and  critical  sharpness  obtained. 
The  most  serious  obstacle  to  sharpness  lies  in  the  films 
themselves.  If  such  a  plate-block  be  outlined,  the  sub- 
ject will  be  more  readily  grasped.  The  front  element 
should  preferably  be  a  glass  plate  with  its  glass  towards 
the  lens,  for  if  films  are  used  it  is  difficult  to  obtain  the 
necessary  flatness  of  the  surface.  Behind  this  front  ele- 
ment is  placed  the  second  sensitive  surface,  and  a  filter 
may  or  may  not  be  interposed;  this  second  element  may 
be  a  film  and  here  the  sensitive  surface  may  face  or  be 
turned  from  the  lens.  The  third  element  is  again  prefer- 
ably a  plate,  as  this  helps  to  keep  the  surfaces  flat;  a 
filter  may  or  may  not  be  interposed  between  the  second 
and  third  films.  The  light  has  to  pass  through  two  sen- 
sitive films  containing  silver  salts  and  these  are  normally 
by  no  means  transparent.  It  is  true  that  the  front  el- 
ement of  the  pack  may  be  one  of  the  transparent  Lipp- 
mann  plates,  as  was  suggested  by  Du  Hauron,  as  this 
is  acted  upon  by  the  blue  rays,  and  can,  therefore,  be 
the  slowest  and  consequently  transparent.  But  when 
we  come  to  the  second  sensitive  surface,  which  is  usually 
devoted  to  the  record  of  the  green  rays,  we  can  no  longer 


TWO-COLOR  PROCESSES  219 

allow  it  to  be  transparent,  for  it  would  be  too  slow. 
Therefore,  it  has  to  be  an  emulsion  of  the  normal  type, 
faster  than  the  front  but  slower  than  the  rear  plate. 
Hence  the  plate  is  more  or  less  translucent  and  the  par- 
ticles of  silver  salt  diffuse  the  light  and  make  it  impos- 
sible to  obtain  in  any  case,  no  matter  how  thin  this  coat- 
ing may  be,  critical  sharpness  on  the  rear  element.  In  the 
case  of  the  two-color  process  we  can  use  a  transparent 
front  plate  and  a  fast  panchromatic  plate  in  the  rear, 
and  obtain  better  results.  There  is  also  another  factor 
that  has  been  ignored  in  the  consideration  of  these  pro- 
cesses, and  that  is  that  the  rear  element,  being  the  one 
on  which  the  red  is  recorded,  that  is,  the  minus-blue 
plate,  is  printed  in  blue.  Now  this  blue  impression  is 
the  one  that  gives  us  what  the  artists  call  the  "drawing" 
of  the  picture.  The  yellow  print  may  be  hopelessly 
out  of  focus,  the  red  less  so,  and  the  results  will  not  be 
objectionable.  But  the  moment  loss  of  sharpness  is 
shown  in  the  blue  it  is  instantly  detected. 

Were  it  possible  to  overcome  this  defect,  the  tri-pack 
or  bi-pack  system  would  be  one  of  the  simplest  to 
use  for  color  photography,  because  the  only  alteration 
needed  in  the  camera  would  be  the  alteration  of  the  plate- 
holder  so  that  it  would  take  two  or  three  plates. 

For  two-color  work,  however,  the  bi-pack  offers  con- 
siderable advantages.  We  can  use  a  slow,  more  or  less 
transparent  chloro-bromide  or  chloride  plate,  and  place 
behind  this  an  orange  filter  and  a  panchromatic  plate. 
If  we  decide  to  use  commercial  niters,  such  as  Wratten 
&  Wainwright,  then  we  can  safely  say  that  the  distance 
between  the  front  and  the  rear  elements  will  be  only  o.i 
mm,  or  approximately  one  two  hundred  and  fiftieth  of  an 
inch,  for  this  is  the  mean  thickness  of  their  gelatine  filters. 


220 


COLOR  PHOTOGRAPHY 


The  best  results  are  obtained  in  two-color  work  by 
using  for  the  two  negatives  the  regions  shown  in  Fig.  26; 
R  represents  those  rays  which  should  act  on  the  pan- 
chromatic plate  and  G  those  for  the  front  plate;  but  un- 
fortunately the  sensitiveness  of  the  normal  chloro-bro- 
mide  plate  is  shown  in  P  by  the  continuous  curve;  while 
that  of  a  chloride  emulsion  is  shown  as  the  dotted  curve. 
There  are  no  commercial  plates  of  either  kind  which  are 


FIG.  26 


color-sensitized,  so  we  should  have  to  sensitize  them. 
The  most  satisfactory  dye  for  this  purpose  would  be 
the  new  German  dye  pinaflavol,  but  whether  this  is  yet 
obtainable  commercially  is  not  known.  This  dye  sensi- 
tizes far  more  satisfactorily  than  all  others  for  just  the 
particular  region  that  we  want  to  record  on  our  front 
element.  But  it  is  also  necessary  to  stain  this  front  plate 
to  cut  out  the  action  of  the  violets  and  deep  blues,  while 
this  new  dye  is  a  basic  dye  and  we  do  not  know  whether 
it  would  stand  admixture  with  a  staining  dye,  which 
must  be  an  acid  dye.  The  sensitizing  and  screening 
dyes  may  be  combined  in  one  bath  and  probably  the 
following  would  be  a  suitable  combination: 


TWO-COLOR  PROCESSES  221 

Erythrosin  o.i  g 

Tartrazin  LO  g 

Distilled  watei  1000  ccm 

Bathe  three  minutes  and  dry  without  washing,  although 
the  plate  should  be  just  rinsed.  Instead  of  tartrazin, 
naphthol  yellow  may  be  used  in  about  the  same  strength. 
The  exact  quantity  of  the  yellow  dye  will  depend  on  the 
results  desired.  The  more  used,  the  more  the  blues  and 
violets  are  cut  out,  and  the  worse  they  will  be  rendered 
in  the  final  picture. 

The  filter  to  isolate  the  red  region  can  be  made  with 
yellowish  eosin  2  g  and  tartrazin  4  g  per  square  meter, 
but  Wratten  &  Wainwright's  No.  22  or  £2  is  suitable. 
This,  of  course,  must  be  the  same  size  as  the  plate  used, 
and  the  rear  plate  must  be  a  panchromatic  plate,  prefer- 
ably backed.  Instead  of  staining  up  the  front  plate, 
a  filter  can  be  placed  on  the  lens;  this  can  be  made  with 
i  g  of  filter  yellow  per  square  meter,  or  either  a 
Wratten  Ki  or  Ki|  can  be  used;  the  former  gives  better 
rendering  of  the  blues. 

There  is  no  need  to  give  instructions  as  to  the  develop- 
ment of  these  plates;  but  a  caution  may  be  necessary 
as  to  the  front  one.  It  may  show  rather  more  contrast 
than  is  desirable  as  compared  with  the  rear  one,  and 
further  it  will  probably  not  stand  such  a  strong  developer, 
and  should  be  developed  separately  in  this  case. 

If  one  decides  to  use  the  tri-pack  system,  then  the  front 
plate  should  be  a  chloro-bromide  or  transparency,  but 
as  it  has  to  record  the  blues  it  should  not  be  stained, 
and  a  yellow  filter  on  the  lens,  such  as  a  Ki,  will  be 
efficient.  The  second  element  has  to  be  the  recorder  of 
the  greens  and  should,  therefore,  be  orthochromatic,  and 


222  COLOR  PHOTOGRAPHY 

as  has  already  been  pointed  out  the  smaller  the  thickness 
of  this  the  better.  Therefore  a  film  should  be  used,  and  the 
ordinary  roll  film  may  be  adopted.  As  a  filter  we  must 
use  one  that  cuts  out  the  blue  and  violet  but  transmits 
the  rest  of  the  spectrum  undamped;  it  is  obvious  that 
we  cannot  use  here  the  normal  green,  as  this  cuts  out 
the  red,  so  we  must  use  a  yellow  such  as  Ka,  which 
has  about  the  right  cut.  Behind  this  middle  element 
we  must  use  a  filter  that  isolates  the  red,  and  the  normal 
tri-color  red  filter  may  be  used  (see  p.  29).  Wratten  & 
Wain wright  No.  25  or  A  is  correct. 

The  tri-pack  will,  therefore,  be  composed  of  the  follow- 
ing, counting  from  the  front  plate  which  faces  to  the  rear: 
a  chloro-bromide  plate  with  glass  towards  the  lens;  a 
Ki|  filter;  a  roll  film  or  orthochromatic  film  with 
the  film  towards  the  lens;  a  standard  tri-color  red  filter; 
a  panchromatic  plate  with  the  sensitive  surface  towards 
the  lens. 

So  far  it  has  been  pretty  easy  sailing,  on  paper,  and  the 
requirements  are  definitely  fixed  and  fairly  easily  satis- 
fied; but  we  now  come  to  the  crux  of  the  whole  matter, 
and  that  is  how  to  adjust  the  sensitiveness  of  the  plates 
and  the  filter  actions  so  that  the  plates  will  all  require 
the  same  exposure.  The  only  thing  to  be  done  is  to  de- 
cide this  by  trial  and  error,  by  photographing  a  scale 
of  greys  with  various  combinations  of  plates  until  the 
scale  is  rendered  alike  on  all  three  members.  Altera- 
tion of  the  filters  is  practically  excluded,  because  this 
would  alter  the  absorptions  and  upset  the  color  rendering. 
The  most  that  one  can  do  with  the  filters  is  to  cut  down 
the  light  with  black  and  this  is  not  an  easy  matter. 

The  tri-pack  system  outlined  above  is  designated  as 
the  dialyte  system,  as  Ducos  du  Hauron  called  his  sug- 


TWO-COLOR  PROCESSES  223 

gested  arrangement  a  "polyfolium  dialyticum."  But 
J.  W.  Bennetto,  in  1897,  suggested  a  semi-dialyte  system, 
in  which  one  plate  receives  one  image  direct,  and  two 
plates  at  right  angles  to  the  former  receive  the  other  two 
images.  This  simplifies  matters  considerably,  and  there 
is  no  reason  why  this  system  should  not  be  more  generally 
adopted.  A  suitable  camera  is  not  on  the  market,  but 
it  would  not  be  a  Difficult  matter  to  make  one.  The  prin- 
ciple is  shown  in  Piig.  27,  in  which  a  represents  the  camera 


FIG.  27 

front,  C  is  a  reflector  at  an  angle  of  45  °  which  throws 
some  of  the  light  to  a2  where  is  placed  a  bi-pack  of  two 
sensitive  plates  with  their  surfaces  hi  contact  with  a 
filter  Dl  in  between,  while  D  is  the  filter  for  the  single 
plate.  Obviously  this  can  be  turned  upside  down  and 
the  two  plates  placed  at  the  bottom  of  the  camera.  There 
is  here  a  choice  as  to  the  division  of  the  plates,  but  per- 
sonally the  writer  would  place  the  red  filter  plate  at  D 
and  the  transparent  chloro-bromide  plate  at  a2,  using  a 
tri-color  green  filter  between  this  and  a  panchromatic 
or  orthochromatic  plate.  In  this  case,  the  reflector 


224  COLOR  PHOTOGRAPHY 

back  must  be  coated  with  a  minus  green  color,  such  as 
fuchsin  or  eosin,  and  the  remarks  on  the  construction 
of  the  camera  on  p.  52  should  also  be  noted  as  to  the 
thickness  of  the  niters,  etc. 

In  this  system,  the  choice  of  plates  and  the  determina- 
tion of  those  most  likely  to  give  equal  exposures  is  con- 
siderably facilitated,  as  one  can  definitely  fix  on  a  pan- 
chromatic for  the  red  and  green  records,  thus  leaving 
only  the  chloro-bromide  for  the  blue  as  the  variable 
factor,  and  one  variable  is  much  easier  to  solve  than 
two.  One  has,  therefore,  far  less  work  in  adjusting  the 
relative  speeds,  because  the  speeds  of  the  panchromatics 
may  be  so  chosen  as  to  be  of  great  assistance  in  adjust- 
ment. One  can  here  use  a  filter  on  the  lens  and  thus 
avoid  staining  up  a  plate,  and  the  standard  tri-color 
filters  may  be  used. 

There  may  be  some  little  trouble  in  registering  the 
plates,  because  of  the  distortion  from  the  reflector,  but 
the  notes  on  p.  55  will  be  of  assistance.  The  registra- 
tion can  be  readily  tested,  as  by  drawing  a  square  with 
diagonal  lines  of  a  goodly  size  and  photographing  down 
it  will  be  easy  to  see  if  the  three  negatives  will  register. 
If  not,  it  is  easy  to  determine  which  one  is  faulty  and 
make  the  corrections  accordingly.  It  may  even  be  nec- 
essary to  distort  the  reflector  slightly  by  packing  the 
edges  with  metal  or  hard  rubber  strips,  but  when  once 
satisfactorily  adjusted  there  should  be  no  need  to  tamper 
with  it  again. 

It  is  obvious  that  in  all  these  processes,  as  one  of  the 
plates  is  placed  with  its  glass  to  the  lens,  the  image  is 
reversed  laterally;  but  this  is  actually  an  advantage  as, 
if  the  pictures  are  used  for  lantern  slides,  this  can  be 
made  on  a  separate  glass  and  used  as  the  cover  glass. 


TWO-COLOR  PROCESSES  225 

If  the  positives  are  to  be  made  by  the  iodide  or  mordant- 
ing process,  it  can  be  easily  reversed,  if  necessary,  in  the 
stripping  process. 

If  the  dialyte  or  semi-dialyte  systems  be  adopted,  the 
printing  colors  are  merely  those  of  the  normal  three- 
color  process,  and  these  have  already  been  dealt  with. 
But  with  a  two-color  system  we  have  to  adopt  a  com- 
promise: practically  we  must  use  a  more  orange  red  and 
a  more  greenish  blue  than  the  standard  three  colors,  but 
any  of  the  actual  printing  methods  may  be  used. 

For  the  diachrome  process  or  those  in  which  basic 
dyes  are  used,  rhodamin  6GF  or  I2GF  may  be  used, 
but  as  there  may  be  difficulty  in  obtaining  these,  one  can 
use  fuchsin  and  auramin  for  the  red  and  malachite  green 
and  auramin  for  the  blue-green.  If  the  relief  or  other 
methods  which  require  acid  dyes  are  used,  then  a  mixture 
of  naphthol  green,  acid  green  and  naphthol  yellow  may  be 
used  for  the  green  and  a  mixture  of  the  acid  reds  with 
naphthol  yellow  for  the  red  picture.  Exact  ratios  of 
the  dyes  cannot  be  given,  but  a  few  trials  will  soon  de- 
termine the  best  composition  to  use;  in  all  cases  the  re- 
sults should  be  examined  by  artificial  light,  for,  as  already 
stated,  two-color  pictures  are  only  satisfactory  when 
thus  viewed.  In  print  making,  the  colors  should  not 
be  too  deep,  as  the  light  has  to  pass  through  the  film 
and  be  reflected  from  the  white  support.  This  obviates 
one  trouble  that  is  frequently  met  in  transparency  making, 
which  is  that  the  deep  shadows  are  sometimes  either  vio- 
let or  red  and  not  black.  This  is  chiefly  due  to  the  faulty 
transmissions  of  the  dyes;  if  the  shadows  are  violet, 
the  red  element  probably  wants  a  little  more  yellow 
in  it,  while  if  they  are  red,  increase  of  the  naphthol  green 
will  cut  this  out. 


226  COLOR  PHOTOGRAPHY 

The  Kodachrome  process  was  introduced  by  the  East- 
man Kodak  Co.  in  1915,  and  is  a  two-color  process  based 
on  the  selective  action  of  dyes  for  hardened  and  un- 
hardened  gelatine.  Like  all  the  other  two-color  pro- 
cesses it  fails  in  the  correct  rendering  of  the  blues,  vio- 
lets, magentas  and  purples;  but  for  flesh  tints,  reds, 
oranges,  greens,  greys  and  blacks  it  is  excellent,  and 
some  exquisite  results  can  be  obtained  if  the  above  limi- 
tations are  borne  in  mind. 

Briefly,  the  method  of  procedure  is  to  expose  two  pan- 
chromatic plates  behind  suitable  color  filters  and,  after 
development,  to  so  treat  the  plates  that  the  gelatine 
is  hardened  in  situ  with  the  metallic  silver  and,  after 
fixing  and  drying,  stain  up  with  the  special  dyes  and 
superimpose.  The  best  effects  are  obtainable  with  arti- 
ficial light  as  the  illuminant. 

The  working  details  follow;  the  two  panchromatic 
plates  can  be  exposed  simultaneously,  which  obviously 
requires  a  special  camera,  or  in  succession.  A  special 
lighting  system  was  devised  by  the  Eastman  Kodak  Co. 
for  portraiture,  though  naturally  daylight  can  be  used. 
The  plates  should  be  developed  with  metol-hydrochinon 
and  the  negatives  should  be  rather  of  a  soft  character, 
which  is  obtainable  as  usual  by  shortened  duration 
of  development;  over-exposure  should  be  avoided  as  far 
as  possible. 

There  are  two  courses  now  open  to  the  worker:  either 
to  fix  the  negatives  in  the  usual  way  and  make  duplicate 
negatives  therefrom,  or  the  less  tedious  plan  of  convert- 
ing the  original  negatives  into  the  dyed  positives.  For 
this  latter  system  the  negatives  should  be  washed  after 
development  for  about  ten  minutes  and  then  bleached 
in  the  following: 


TWO-COLOR  PROCESSES  227 

A.  Potassium  ferricyanide  37.5    g 
Potassium  bromide  56.25  g 
Potassium  bichromate                   37.5    g 
Glacial  acetic  acid  10  ccm 
Water                                              1000  ccm 

B.  Potassium  alum,  5  per  cent  solution. 

For  use,  mix  in  equal  volumes.  Care  must  be  taken  to 
cover  the  plate  with  one  sweep  of  the  bath  and  use  not 
less  than  250  ccm  for  500  square  centimeters.  The  bleach- 
ing will  take  approximately  four  minutes,  and  the  ac- 
tion should  be  allowed  to  continue  for  a  short  time  after 
all  the  black  silver  has  disappeared,  it  being  converted 
into  a  brown  image.  The  plate  should  then  be  washed 
for  ten  minutes  in  running  water  and  fixed  in  a  bath 
that  does  not  contain  alum,  such  as: 

A.  Hypo  250  g 
Water  1000  ccm 

B.  Sodium  bisulphite  400  g 
Water  1000  ccm 

For  use,  mix  i  part  of  B  with  20  parts  of  A.  This  may  be 
used  repeatedly  but  not  for  more  than  3400  square  centi- 
meters per  liter  (2000  square  inches  per  gallon). 

At  this  stage  the  plates  look  perfectly  transparent 
with  no  sign  of  an  image,  and  should  be  washed  for 
twenty  minutes  and  then  immersed  in  a  0.5  per  cent 
solution  of  ammonia  and  the  dish  well  rocked  for  three 
minutes,  and  again  washed  for  another  five  minutes.  Sur- 
face moisture  should  be  removed  with  a  soft  squeegee  or 
by  dabbing  the  plate  with  a  pad  of  fluffless  cloth,  and 
the  back  must  be  dried.  Drying  must  be  uniform  and 
the  best  plan  is  to  dry  before  an  electric  fan.  If  the  plates 


228  COLOR  PHOTOGRAPHY 

dry  in  patches,  these  will  show  in  the  finished  picture. 
The  drier  the  film  the  cleaner  the  high-lights,  and  the 
plates  may  be  dried  in  an  oven  or  left  for  at  least  three 
hours  after  drying  in  the  usual  way.  This  latter  plan 
requires  longer  development,  and  the  longer  they  are 
left  after  drying  and  before  staming  up  the  greater  the 
contrasts  in  the  resultant  picture,  so  that  it  uniformity 
is  required  constant  conditions  must  be  observed. 

Special  dyes  are  issued,  and  a  1.2  per  cent  solution  of 
the  red  dye  and  a  three  per  cent  solution  of  the  green 
dye  should  be  prepared.  It  is  advisable  to  dissolve 
the  dyes  in  a  little  hot  water  and  filter  the  solutions 
through  linen  after  dilution  to  bulk;  distilled  water 
should  be  used.  The  complementary  colors  are  used, 
of  course;  that  is,  the  negative  taken  through  the  red 
filter  is  dyed  green,  and  that  of  the  green  filter  dyed  red. 
The  dye  solutions  may  be  used  repeatedly  but  should  be 
kept  up  to  strength  by  addition  of  fresh  dye  from  time 
to  time.  As  soon  as  the  plates  are  immersed  in  the  dye 
solutions  the  surfaces  should  be  gently  rubbed  with  a 
tuft  of  absorbent  cotton  to  remove  any  air-bells.  The 
average  time  of  dyeing  is  about  three  minutes,  but  the 
progress  may  be  watched  by  rinsing  the  plates  with  water, 
although  it  is  not  advisable  to  resort  to  this  too  often. 
Naturally  they  must  be  examined  by  the  light  by  which 
they  are  subsequently  to  be  viewed.  If  the  composite 
picture  shows  a  predominance  of  one  color,  the  com- 
plementary plate  should  be  more  deeply  stained.  As 
soon  as  the  plates  are  considered  sufficiently  stained, 
rinse  them  in  a  i  per  cent  solution  of  glacial  acetic  acid, 
and  wipe  the  surface  of  the  film  as  already  advised.  It 
is  important  that  the  plates  should  dye  quickly;  the 
green  plate  dyes  more  slowly  than  the  red,  but  even  so 


TWO-COLOR  PROCESSES  229 

should  not  take  more  than  ten  minutes;  if  it  does  the 
temperature  of  the  dye  baths  should  be  slightly  raised. 
Slow  dyeing  is  also  caused  by  insufficient  bromide  in 
the  developer  and  overexposure. 

To  superimpose  the  plates,  the  green  image  should  be 
placed  on  top  of  the  red  image  and  shifted  about  until 
perfect  registration  is  obtained.  Then  the  sides  of  the 
plates  should  be  clipped  together  by  large  metal  clips 
and  short  paper  clips  applied  and  these  allowed  to  dry. 
If  a  mask  is  to  be  used  it  should  be  now  applied  on  top 
of  the  green  plate  under  the  cover  glass  and  the  three 
plates  bound  up  with  long  binding  strips.  Retouching 
may  be  effected  with  the  dye  solutions  thickened  with 
gum  arabic  solution. 

If  the  duplicate  negative  method  is  adopted,  and  it 
is  advantageous  for  several  copies,  then  the  original 
negatives  are  fixed,  washed  and  dried  in  the  usual  way 
and  from  these  transparencies  made,  and  duplicate  neg- 
atives; the  best  plates  for  both  purposes  being  those 
of  the  character  of  the  Seed  23.  Both  plates  should  be 
exposed  at  the  same  time  at  the  same  distance  from  the 
light,  and  developed  together,  aiming  at  fully  exposed, 
soft,  delicate  negatives  with  all  the  detail  of  the  original 
negatives;  the  further  treatment  is  precisely  as  has  been 
detailed  above  for  the  original  negatives. 


CHAPTER  XIX 
CINEMATOGRAPHY  IN  COLORS 

THE  combination  of  the  illusion  of  movement  given 
by  the  motion  picture  with  colors  has  been  for  many 
years  the  hope  of  numerous  inventors.     But  a  brief 
sketch  of  their  work  can  be  given,  as  it  would  require  a 
treatise  larger  than  this  book  to  exhaust  the  subject. 

The  fundamental  basis  of  the  motion  picture  is  the 
phenomenon  of  persistence  of  vision.  A  bright  light  pro- 
duces on  the  retina  a  certain  impression,  which  lasts  as 
long  as  the  light  is  burning  and  a  little  longer,  that  is  to 
say,  the  sensation  of  light  is  not  instantaneously  wiped 
out.  If  a  succession  of  pictures  be  rapidly  projected, 
about  sixteen  per  second,  the  impression  of  the  first  pic- 
ture persists  on  the  retina  until  the  second  one  is  also 
there  and  is  superimposed,  and  the  same  with  succeeding 
pictures;  therefore  we  have  the  impression  of  a  complete 
picture,  the  sum  of  the  individual  phases  of  a  move- 
ment, etc. 

Precisely  the  same  thing  occurs  with  colors,  The  rapid 
alternation  of  red  and  green  gives  us  the  impression  of 
yellow,  of  the  constituents  of  which  we  are  no  longer  con- 
scious; so  if  a  succession  of  red,  green  and  blue  pictures 
are  rapidly  and  alternately  presented  to  the  retina,  the 
composite  result  will  be  a  moving  picture  in  colors.  The 
first  suggestion  as  to  such  a  process  was  made  by  H.  Isen- 
see,  a  German,  in  1897,  although  Cros  in  1867  had  sug- 
gested the  synthesis  of  a  single  picture  by  this  method. 
230 


CINEMATOGRAPHY  IN  COLORS         231 

Isensee  proposed  to  take  the  pictures  through  the  tri- 
color filters  and  project  them  in  the  same  way.  Several 
inventions  were  patented  in  which  the  same  idea  was 
involved;  but  the  great  disadvantage  of  this  process, 
and  in  fact  of  all  processes  in  which  different  phases  of 
a  movement  are  represented  in  different  pictures,  is  that 
one  cannot  obtain  a  perfect  composite  result.  This  is 
clearly  seen  if  one  imagines  the  use  of  the  three-color 
filters  with  successive  exposures  of  a  very  simple  object; 
assume  that  a  man  is  holding  his  arm  at  right  angles  to 
his  shoulder  and  drops  it  to  his  side,  and  that  during  the 
movement  of  the  arm  we  take  three  pictures.  It  is  ob- 
vious that  we  have  a  red  picture  of  the  arm  in  one  po- 
sition, a  green  picture  of  the  arm  in  another  position 
and  a  blue  picture  in  another.  It  is  impossible  to  reg- 
ister these,  and  they  will  not  superimpose  sufficiently 
well  on  the  retina  to  be  sharp;  we  shall  see  the  arm  first 
with  a  red  fringe  at  the  top,  then  with  a  green  fringe  at 
the  top  and  a  blue  fringe  at  the  bottom  and  so  on,  so 
that  a  sharp  single  picture  by  this  method  is  impossible. 

Another  and  very  serious  defect  is  technically  known 
as  color  bombardment.  This  is  the  physical  effect  pro- 
duced by  the  rapid  alternation  of  the  colors.  With  some 
people  this  produces  intense  discomfort  and  severe 
frontal  headache.  It  is  probably  due  to  the  imperfect 
achromatism  of  the  eye,  for  while  the  mam  effect  on  the 
screen  is  a  homogeneous  color,  yellow,  for  instance,  in 
the  alternation  of  red  and  green,  yet  there  is  a  peculiar 
pulsation  or  throbbing  which  is  not  flicker  and  yet  is 
closely  allied  to  it. 

These  troubles  led  to  attempts  to  take  and  project 
the  three  constituent  pictures  at  once,  so  that  each  pic- 
ture was  complete  in  itself  as  regards  color.  While 


232  COLOR  PHOTOGRAPHY 

this  obviated  the  color  bombardment  trouble,  it  intro- 
duced other  troubles  in  the  necessity  for  special  optical 
devices,  which  not  only  are  costly  but  in  the  use  of  which 
one  is  much  hampered  by  the  fact  that  the  average  cine- 
matographic lens  ranges  from  two  to  three  inches  in  focal 
length,  and,  therefore,  one  is  cramped  for  room.  If  more 
than  one  lens  be  used,  that  is,  either  two  or  three  verti- 
cally or  horizontally  disposed,  the  element  of  parallax 
is  introduced,  which  is  also  sometimes  called  stereo- 
scopic parallax.  Exactly  the  same  phenomenon  appears 
in  our  own  vision;  each  eye  sees  a  slightly  different  view 
of  an  object  and  all  objects  beyond  the  particular  plane 
focused  on  appear  double  and  wanting  in  sharpness. 
This  can  easily  be  seen  by  holding  a  pencil  or  some  such 
object  at  about  ten  inches  from  the  eyes  and  focusing 
them  on  it,  the  background  being  a  window  with  cross 
bars  about  a  yard  away.  When  the  pencil  is  sharply 
focused  the  window  bars  will  be  found  to  be  double,  and  if 
the  bars  are  focused  the  pencil  will  appear  as  two.  We 
are  not  conscious  of  this  ordinarily,  as  the  eye  automat- 
ically focuses  itself  and  ranges  over  the  whole  field  of 
vision,  so  that  we  obtain  the  sum  of  the  individual  im- 
pressions. In  the  case  of  the  cinematographic  camera, 
there  is  no  variation  of  focus,  so  that  parallax  or  the 
doubling  of  near  or  distant  objects  is  distinctly  seen. 

Another  trouble  which  is  purely  a  mechanical  one  is 
that  the  normal  rate  of  taking  pictures,  and  exhibiting 
them,  is  sixteen  per  second.  If  the  single  objective  be 
used,  the  film  has  to  travel  three  times  as  fast  as  for 
black  and  white.  If  three  juxtaposed  lenses  be  used 
vertically,  one  has  to  make  the  film  travel  three  picture 
spaces  at  each  exposure,  and  if  they  are  horizontally 
juxtaposed,  then  triple  width  nlm  must  be  used. 


CINEMATOGRAPHY  IN  COLORS         233 

These  difficulties  led  G.  A.  Smith  in  1907  to  revert 
to  a  two-color  process,  in  which  alternating  pictures 
were  taken  and  projected  through  a  rotating  shutter 
with  red  and  green  sectors.  This  process  was  known  as 
Kinemacolor  and  some  excellent  results  were  shown.  But 
this  process  was  handicapped  by  color  bombardment. 
It  was  simpler  than  those  processes  in  which  simul- 
taneous projection  of  the  constituent  color  pictures  is 
used,  as  the  only  extra  fitting  for  the  projector  was  the 
rotating  shutter,  and  possibly  a  few  gear  wheels  to  speed 
up  the  travel  of  the  film.  It  may  be  accepted  as  an  axiom 
that  any  process  that  requires  a  special  projector  or 
special  fittings  is  hopelessly  out  of  the  commercial  running. 

The  Smith  system  was  based  on  the  fact  that  in  tri- 
color projection,  the  blue-violet  constituent  adds  but 
little  color  as  such.  It  brightens  up  the  other  colors 
and  forms  white.  It  does  provide  the  pure  blues  and  vio- 
lets. But  white  is  but  a  relative  term  and  we  accept  as 
white  in  two-color  projection  that  which  is  actually  a 
yellow.  The  process  was  actually  an  additive  one,  and 
the  black  and  white  positives  were  projected  through  red 
and  green  filters,  which  were  not  of  quite  the  same  shade 
as  the  taking  filters. 

At  the  present  time  the  efforts  of  most  inventors  seem 
to  be  directed  to  the  production  of  subtractive  pictures, 
in  which  each  picture  is  itself  a  complete  color  record, 
and  although  but  two  colors  are  used  the  results  in  many 
cases  are  extremely  pleasing.  That  the  colors  are  abso- 
lutely true  cannot  be  upheld,  but  the  lack  is  so  small 
that  the  average  observer  can  rarely  detect  it.  Moreover 
the  question  of  color,  whether  in  an  oil  painting  or  a  photo- 
graph in  colors,  is  so  much  a  matter  of  individual  feeling 
that  probably  no  two  critics  would  be  in  strict  accord 


234  COLOR  PHOTOGRAPHY 

as  to  the  correctness  of  a  particular  color   rendering. 

The  processes  that  are  used  are  to  some  extent  se- 
crets; but  they  would  all  be  found  to  fall  into  the  relief 
or  mordanting  methods  already  described.  The  use  of 
double-coated  film,  that  is,  film  with  emulsion  on  both 
sides,  is  fairly  general.  While  this  facilitates  the  process 
hi  that  one  has  two  distinct  images  that  can  be  appro- 
priately colored,  it  introduces  other  troubles  in  the  shape 
of  rigorous  necessity  of  registration,  and  it  is  obvious 
that  care  has  to  be  exercised  that  each  image  is  confined 
to  one  side  of  the  emulsion. 

The  production  of  motion  pictures  in  colors  offers  an 
enticing  field  for  the  experimenter,  but  it  is  beyond  the 
reach  of  the  average  worker,  as  the  outlay  for  the  appa- 
ratus is  heavy.  Should  anyone  be  desirous  of  entering  this 
field,  the  soundest  advice  that  can  be  given  is  to  study 
the  two  or  three  hundred  patents  that  have  been  issued 
on  the  subject,  as  no  practical  details  have  yet  found 
their  way  into  print.  It  should  be  borne  in  mind  that 
a  subtractive  process  with  the  colors  on  each  picture  on 
a  single  film  that  can  be  run  through  any  projector  is 
the  desideratum. 

Whether  a  three-color  subtractive  film  is  within  rea- 
sonable reach  of  perfection  is  not  known;  but  there  are 
two  or  three  two-color  subtractive  processes  which 
threaten  to  become  commercial  within  a  reasonable 
tune.  Even  if  the  cost  of  the  production  of  the  film  can 
be  kept  down  within  reasonable  limits,  because  after 
all  this  is  an  important  question,  it  is  a  debatable  point 
whether  the  public  is  sufficiently  educated  to  pay  more 
for  seeing  pictures  in  colors,  and  whether  it  would  be  more 
attractive  to  the  multitude  to  see  Charlie  Chaplin  fooling 
in  colors  than  in  black  and  white. 


CONVERSION    OF    WEIGHTS    AND    MEASURES 

The  following  tables  are  sufficient  to  enable  anyone 
to  readily  convert  the  metric  into  the  customary  units, 
and  are  based  on  those  published  by  the  U.  S.  Bureau 
of  Standards 

LENGTHS 


Inches 

Centimeters 

Inches 

Centimeters 

0-3937 

=  i 

i 

=   2.5400 

0.7874 

=  2 

2 

=   5.0800 

1.1811 

=  3 

3 

=   7.6200 

1.5748 

=  4 

4 

=  10.1600 

1.9685 

=  5 

5 

=  12.7000 

2.3622 

=  6 

6 

=  15.2400 

2-7559 

=  7 

7 

=  17.7800 

3.1496 

=  8 

8 

=  20.3200 

3-5433 

=  9 

9 

=  22.8600 

AREAS 

Square 
Inches 

Square 

Centimeters 

Square 
Inches 

Square 
Centimeters 

0.1550 

=  i 

i 

=   6.452 

0.3100 

=  2 

2 

=  12.903 

0.4650 

=  3 

3 

=  19-355 

0.6200 

=  4 

4 

=  25.807 

0.7750 
0.9300 
1.0850 

=  5 
=  6 

=  7 

5 
6 

7 

=  32.258 
=  38.710 
=  45.161 

1.2400 

=  8 

8 

=  5i-6l3 

1-3950 

=  9 

9 

=  58.065 

235 


236 


COLOR  PHOTOGRAPHY 


MASSES 


Grains 

Grams 

Grains 

Grams 

i 

=0.0648 

I5-4324 

=  i 

2 

=0.1296 

30.8647 

=  2 

3 

=0.1944 

46.2971 

=  3 

4 

=0.2592 

61.7294 

=  4 

5 

=0.3240 

77.1618 

=  5 

6 

=0.3888 

92.5941 

=  6 

7 

=0.4536 

108.0265 

=  7 

8 

=  0.5184 

123.4589 

=  8 

9 

=0.5832 

138.8912 

=  9 

LIQUIDS 

Cubic 

Cubic 

Fluid 

Centimeters             Minims 

Centimeters 

Ounces 

i 

=  16.230 

29.574 

=  i 

2 

=  32.460 

59.147 

=  2 

3 

=  48.690 

88.721 

=  3 

4 

=  64.920 

118.295 

=  4 

5 

=  81.150 

147.869 

=  5 

6 

=  97.380 

177.442 

=  6 

7 

=  113.610 

207.016 

=  7 

8 

=  129.840 

236.590 

=  8 

9 

=  146.070 

266.163 

=  9 

The  U.  S. 

gallon  =  3785.43  ccm; 

one  liter  =  33 

fld.  oz., 

391  mnms. 

The  above  tables  apply  to  the  English  weights  and 
measures,  with  the  exception  of  the  liquid  measures; 
the  English  gallon  measures  160  fld.  oz.  =  4545.96  ccm. 


WEIGHTS  AND  MEASURES  237 

The  following  therefore  must  be  used  for  conversion  of 
the  same. 


Cubic 

Cubic 

Fluid 

Centimeters 

Minims 

Centimeters 

Ounces 

i 

=   16.894 

28.4123 

=  i 

2 

=  33.788 

56.8245 

=  2 

3 

=  50.682 

85.2368 

=3 

4 

=  67.576 

113.6400 

=  4 

5 

=  84.470 

142.0613 

=  5 

6 

=  101.364 

I70-4735 

=  6 

7 

=  118.258 

198.8858 

=  7 

8 

=  i35-i52 

227.2980 

=  8 

9 

=  153.046 

255-7I03 

=  9 

BIBLIOGRAPHY 

On  the  theory  of  color  and  color  vision  generally,  the 
following  works  should  be  consulted: 

Color  Measurement  and  Mixture.  W.  Abney. 
London.  1891. 

Textbook  of  Color.    O.  N.  Rood.    New  York.     1913. 

Colour.    A.  H.  Church.    London.     1911. 

Color  and  its  Applications.  M.  Luckiesh.  New 
York.  1915. 

General  books  on  color  photography. 

Photography  in  Colours.  T.  Bolas,  A.  A.  K.  Tallent 
and  E.  Senior.  London.  1900. 

Photography  in  Colors.  G.  L.  Johnson.  London. 
1914. 

Natural-Color  Photography.  E.  Konig  and  E.  J. 
Wall.  London.  1906. 

Three-Color  Photography.  Von  Hubl  and  H.  0.  Klein. 
London.  1915. 

Color-Photography.  C.  E.  K.  Mees.  Photo-Miniature 
No.  183.  New  York.  1921. 

Die  Grundlagen  der  Farbenphotographie.  B.  Donath. 
Brunswick.  1906. 

Die  Dreifarbenphotographie.   Von  Hubl.   Halle.    1921. 

Die  Dreifarbenphotographie  nach  der  Natur.  A. 
Miethe.  Halle.  1904. 

Die  Darstellung  der  natiirlichen  Farben.  H.  Krone. 
Weimar.  1894. 

238 


BIBLIOGRAPHY  239 

Die  Photographic  in  naturlichen  Farben.  E.  Valenta. 
Halle.  1912. 

La  Reproduction  photographique  des  Couleurs.  H. 
Calmels  and  L.  P.  Clerc.  Paris.  1007. 

La  Triplice  photographique  des  Couleurs.  A.  Ducos 
du  Hauron.  Paris.  1897. 

Les  Couleurs  et  la  Photographie.  G.  H.  Niewenglow- 
ski  and  A.  Ernault.  Paris.  1895. 

Les  Couleurs  reproduites  en  Photographie.  E.  Du- 
moulin.  Paris.  1894. 

Photographie  des  Couleurs.    L.  Vidal.    Paris.    1897. 

Traite  pratique  de  Photochromie.  L.  Vidal.  Paris. 
1903. 

On  sensitizing  plates,  and  filters: 

Die  orthochromatische  Photographie.  Von  Hiibl. 
Halle.  1920. 

Manuel  pratique  d'orthochromatisme,  L.  Vidal. 
Paris.  1891. 

Das  Arbeiten  mit  farbenempfindlichen  Platten.  E. 
Konig.  Berlin.  1912. 

Die  photographischen  Lichtfilter.  Von  Hiibl.  Halle. 
1910. 

On  screen-plates: 

Die  Autochrom-photographie.   E.  Konig.   Berlin.  1008. 

Die  Theorie  und  Praxis  der  Farbenphotographie  mit 
Autochromplatten.  Von  Hiibl.  Halle.  1909. 

Farbenphotographie  mit  Farbrasterplatten.  A. 
Mebes.  Bunzlau,  1911. 

On  the  bleach-out  process: 

Das  Ausbleichverfahren.    F.  Limmer.    Halle.     1911. 


240  COLOR  PHOTOGRAPHY 

On  Lippmann's  process: 

Die  Farbenphotographie  nach  Lippmanns  Verfahren. 
R.  Neuhauss.  Halle.  1898. 

Beitrage  zur  Theorie  und  Praxis  der  direkten  Farben- 
photographie. H.  Lehmann.  Freiburg.  1906. 

La  Photographic  directe  des  Couleurs  par  le  precede 
Lippmann.  G.  H.  Niewenglowski  and  A.  Ernault. 
Paris.  1895. 

Manuel  de  Photochromie  interferentielle.  A.  Berthier. 
Paris.  1895. 

On  the  Seebeck  process: 

Lehrbuch  der  Photochromie.  W.  Zenker.  Brunswick. 
1900. 

Photomechanical  work: 

Die  Autotypie  und  der  Dreifarbendruck.  H.  K. 
Broum.  Halle.  1912. 

Les  Reproductions  photomechaniques  polychromes. 
L.  P.  Clerc  and  H.  Calmels.  Paris.  1919. 


POSSIBLE  SOURCES  OF  VARIOUS  DYES 

(Where  no  names  are  given  the  dye  is  sufficiently  common  to  be 
obtained  from  almost  any  maker.) 

Acid  green  JE.    Sherwin  Williams  Co.,  n  Stillings  St.,  Boston. 
Acid  yellow.    National  Aniline  &  Chemical  Co.,  21  Burling  Slip, 

New  York. 
Acid  rhodamin.    H.  A.  Metz  &  Co.,  Inc.,  122  Hudson  Street, 

New  York. 

Aesculin.    Merck  &  Co.,  45  Park  Place,  New  York. 
Alizarin-cyanol.     Cassella. 
Auramin.    Eastman  Kodak  Co.,    Rochester,  N.  Y.    A  pure  variety 

is  sold  under  the  name  of  Pyoktanin  aureum  by  Merck  &  Co. 
Aurantia. 
Aurophenin.    National  Aniline  &  Chemical  Co.;  E.  I.  du  Pont  de 

Nemours  &  Co.,  Inc.,  Wilmington,  Del. 

Bluish  acid  green.     Sherwin  Williams  Co.,  Bachmeier  &  Co. 
Bluish  fast  green.    Sherwin  Williams  Co.,  Bachmeier  &  Co. 

Carmin.    Any  drug  store. 

Carmine  blue.     Merck  &  Co. 

Chrysoidin  Y.      Bachmeier  &  Co.,  261  Franklin  St.,  Boston,  Mass. 

Chrysophenin.     National  Aniline  &  Chemical  Co. 

Crystal  violet.     H.  A.  Metz  &  Co. 

Curcumin.     Eastman  Kodak  Co. 

Cyanin.    H.  A.  Metz  &  Co. 

Diamin    blue.     National    Aniline    &    Chemical    Co.,    Schoelkopff 
Branch,  Buffalo,  N.  Y.    Sold  as  Niagara  blue  46. 

Eosin,  yellowish. 
Erythrosin. 

Fuchsin.    Bachmeier  &  Co. 

Glycin  red.    Kinzelberger,  Prag,  Czechoslovakia. 

Indulin  blue.    Bachmeier  &  Co. 

Janus  red  B.    H.  A.  Metz  &  Co. 

Lanafuchsin.    Cassella. 

Malachite  green.    Eastman  Kodak  Co. 
Methylene  blue.    Eastman  Kodak  Co. 
241 


242     POSSIBLE  SOURCES  OF  VARIOUS  DYES 

Methyl  violet. 

Mikado  yellow.    H.  A.  Metz  &  Co. 

Naphthol  green.    Bachmeier  &  Co. 
Naphthol  yellow. 

Orthochrom  T.      Eastman  Kodak  Co. 

Patent  blue.    H.  A.  Metz  &  Co. 

Pinachrom.    H.  A.  Metz  &  Co. 

Phenosafranin.     Bachmeier  &  Co. 

Pinaflavol.    H.  A.  Metz  &  Co. 

Ponceau. 

Primrose.    Also  sold  as  naphthol  yellow  by  most  makers. 

Prussian  blue.    Merck  &  Co. 

Pyronin  G.    National  Aniline  &  Chemical  Co. 

Quinolin  yellow.    H.  A.  Metz  &  Co. 

Safranin  Y.    Bachmeier  &  Co. 

Sensitol  green  &  violet.    Ilford,  Ltd.,  Ilford,  London,  England. 

Tartrazin. 

Thionin  blue.    H.  A.  Metz  &  Co. 

Toluidin  blue.    H.  A.  Metz  &  Co. 

Vesuvin.    Sold  as  Bismarck  brown. 
Victoria  blue  B. 

Xylene  red  B.    H.  A.  Metz  &  Co. 


INDEX 


Absorption,  2. 

Absorption  bands,  4. 

Absorption,  selective,  2,  4. 

Acid  dyes,  97. 

Action  of  bromides,  48. 

Actinometer,  63. 

Additive  filters,  24. 

Additive  processes,  10,  24. 

Adurol,  151. 

Aesculin,  143. 

Albumen  process,  189. 

Alcohol  sensitizer,  62. 

Alizarin  crimson,  112. 

Alkaline  fluorides,  106. 

Aluminum  screens,  166. 

Amidol,  151. 

Amplitude  of  waves,  187. 

Andresen,  88. 

Anethol,  182. 

Angstrom  units,  186. 

Artificial  light,  158. 

Autochrome,      hypersensitizing, 

148. 

Autochrome  emulsion,  147. 
Autochrome  plate,  137. 

Backing,  black,  20. 
Backed  plates,  20. 
Backs,  sliding,  38. 
Basic  dyes,  97. 
Bawtree,  A.  E.,  123. 
Becquerel,  E.,  200. 
Belitski's  reducer,  93. 
Bennetto,  J.  W.,  223. 
Bibliography,  238. 
Bichromate  reliefs,  85. 
Bichromate  reverser,  151. 
Bi-gum  process,  no. 
Bi-pack,  217. 
Black  backing,  20. 
Black  specks,  163. 


Bleach-out  collodion,  183. 
Bleach-out  process,  171,  179. 
Bleach-out  sensitizers,  182. 
Bleeding  of  dyes,  98. 
Blue  filter,  23,  30. 
Branfill,  J.  A.  C.,  213. 
Bromide,  action  of,  48. 
Butler,  J.  W.,  50. 

Cameras,  50. 

Camera,  semi-dialyte,  55,  223. 
Canada  balsam,  26,  35. 
Carbon  process,  60. 
Carbon  sensitizer,  62. 
Carbons,  developing,  67. 
Carbons,  superposition  of,  70. 
Celluloid  sheets,  66. 
Celluloid  sensitizing,  118. 
Celluloid  varnish,  82,  no. 
Cementing  filters,  34. 
Cement,  gelatine,  109. 
Cementing  pictures,  108. 
Chemical  toning,  102. 
Cheron,  F.,  212. 
Chloranol,  151. 
Chrome  fixing  bath,  49. 
Chrome  yellow,  112. 
Chromoscope,  125. 
Chromoscope  filters,  130. 
Chromoscope  mirrors,  132. 
Cinematography  in  colors,  230. 
Cleaning  glass,  30. 
Coating  celluloid,  117. 
Coating  gum-bichromate  paper, 

114. 

Collodion,  bleach-out,  183. 
Collodion  emulsion,  39,  201. 
Color  bombardment,  231. 
Color  diaphragm,  213. 
Color  filters,  22,  25. 

of,  i. 


Color,  formation 


243 


244 


INDEX 


Color  fringes,  231. 
Color  printing,  79. 
Color  projection,  164. 
Color  sensation  curves,  22. 
Color,  subtractive  printing,   24. 
Colored  reflector,  51. 
Colors,  complementary,  5. 
Colors,  fundamental,  6. 
Colors,  primary,  6. 
Combination  of  processes,  104. 
Combination  slides,  125. 
Combined  screen-plate,  140. 
Commercial  niters,  33. 
Commercial  plates,  19. 
Compensating  filter,  55,  142. 
Complementary  colors,  5. 
Composition  of  daylight,  57. 
Contrast,  40. 
Copper  intensifier,  156. 
Copper  mordanting,  99. 
Correcting  pinatype  prints,  82. 
Correction  filter,  165. 
Cramer  plates,  20. 
Cros,  Chas.,  50,  75,  179,  212,  230. 
Cross-line  screen,  213. 
Cutting  screen-plates,  177. 
Cyanotype  toning,  103. 
Cyanotype  transparencies,  124. 

Dark  room,  41. 
Daylight,  composition  of,  57. 
Decolorization  of  isocyanins,  17. 
Decolorizing  print-plates,  80. 
Desensitizing,  43,  148. 
Developed  relief  processes,  92. 
Developer,  temperature  of,  48. 
Developing  carbons,  67. 
Developing  bi-gum  prints,  114. 
Development,  duration  of,  150. 
Development,  second,  153. 
Development    of    screen-plates, 

148. 

Development,  velocity  of,  40. 
Diachrome  process,  95,  225. 
Dialyte  system,  223. 
Diaphragm,  213. 
Didier,  L.,  76. 
Diffraction  grating,  205. 
Diffraction  process,  205. 


Dispersion,  prismatic,  212. 

Distortion,  filter,  26. 

Double  reflection,  27. 

Drac,  J.,  212. 

Draper,  J.  W.,  200. 

Drying  apparatus,  14. 

Drying  films,  35. 

Drying  filters,  32. 

Drying  plates,  18. 

Drying  screen-plates,  156. 

Du  Hauron,  136,  179,  217,  222. 

Duration  of  development,  150. 

Dye  bleeding,  98. 

Dye  intensification,  123. 

Dye  fixing  bath,  98. 

Dye,  panchromatizing,  15. 

Dyes: 

acid  green  JE,  172. 

acid  yellow,  79,  87. 

acid  rhodamin,  26. 

aesculin,  143. 

alizarin  cyanol,  87. 

auramin,  97,  180,  183,  225. 

aurantia,  148. 

aurophenin,  122. 

bluish  acid  green,  42. 

bluish  fast  green,  123. 

carmine,  78. 

carmine  blue,  87. 

chrysoidin  ¥,97. 

chrysophenin,  122. 

crystal  violet,  54,  172 

curcumin,  183. 

cyanin,  190. 

diamin  blue  38,  87. 

diamin  blue  FF,  122. 

eosin,  yellowish,  173. 

erythrosin,  87,  121,  221. 

erythrosin,  bluish,  180. 

fuchsin,  87,  225. 

glycin  red,  190. 

indulin  blue,  79. 

isocyanin,  16. 

janus  red  B,  97. 

kodachrome,  229. 

lanafuchsin  B  B  S  L,  78. 

malachite  green,  225. 

methylene  blue,  54,  97.  '• 

methylene  blue  BB,  180 


INDEX 


245 


methyl  violet,  172. 
mikado  yellow,  79,  122. 
naphthol  green,  26,  42,  172. 
naphthol  yellow,  87. 
naphthol  yellow  S,  122. 
night  blue,  97. 
patent  blue,  26,  54. 
patent  blue  V,  122. 
phenosafranin,  54,  143. 
pinachrom,  193. 
pinaflavol,  220. 
ponceau,  87. 
primrose,  183. 
Prussian  blue,  112. 
pyronin  G,  97. 
quinolin  yellow,  79. 
rhodamin  B,  123. 
rhodamin  G,  87. 
rhodamin  6GF,  I2GF,  225. 
rose  Bengal,  25,  54,  171. 
safranin  Y,  97. 
sensitol  green,  193. 
sensitol  violet,  15,  39,  193. 
tartrazin,  26,  42,  143,  171,  221 
thioflavin,  97. 
thionin  blue,  97. 
toluidin  blue,  26,  54. 
vesuvin,  97. 

victoria  blue  B;  97,  183. 
xylene  red  B,  123. 

Eastman  Kodak  Co.,  20,  226. 
Edwards,  E.,  75. 
Emulsion,  collodion,  39. 
Emulsion,  gelatine,  119. 
Etching  process,  88. 
Ether  vibrations,  186. 
Exhibiting  screen-plates,  164. 
Expansion  of  paper,  104. 
Exposure  ratios,  55. 
Exposure  of  screen-plates,  146. 

Failures,  159. 
Farmer,  Howard,  71,  84. 
Farmer's  reducer,  93. 
Ferric  oxalate,  102. 
Ferric  oxalate  reducer,  93. 
Film  sensitizing,  21. 
Filters,  additive,  24. 


Filter,  blue,  23,  30. 

Filter,  cementing,  34. 

Filter,  compensating,  55,  142. 

Filter  distortion,  26. 

Filter  fitting,  36. 

Filter,  green,  23,  30. 

Filter  making,  29. 

Filter,  minus  green,  54. 

Filter  position,  36,  143. 

Filter,  monobromfluorescein,  54. 

Filter  ratios,  57. 

Filter,  red,  29,  23. 

Filter,  size  of,  27. 

Filter  thickness,  52. 

Filter  transmissions,  25. 

Filter,  tri-color  green,  54. 

Filters,  chromoscope,  130. 

Filters,  color,  22. 

Filters,  commercial,  33. 

Filters,  drying,  32,  35. 

Filters,  liquid,  25. 

Filters,  screen-plate,  144. 

Filters,  sharp-cut,  171. 

Filters,  stripping,  33. 

Final  pinatype  support,  80 

Final  support,  69. 

Fitting  for  filters,  36. 

Fixing  bath,  49. 

Fixing  bleach-out  prints,  184 

Fixing  heliochromes,  196. 

Fixing  pinatype  prints,  83. 

Fixing  screen-plates,  156. 

Flats,  optical,  38. 

Flashlight,  145. 

Flashlight  mixtures,  158. 

Fluorides,  alkaline,  106. 

Formaldehyde  stripping,  107 

Fraunhofer  lines,  2,  6,  185. 

Fundamental  colors,  6,  22. 

Gamma,  40. 
Gelatine  cement,  109. 
Gelatine  emulsion,  190. 
Glass,  cleaning,  30. 
Glass,  oiling,  31. 
Glass,  tacky,  117. 
Goethe,  200. 
Grating,  diffraction,  205. 
Grating  rulings,  207. 


246 


INDEX 


Gratings,  printing  from,  207. 
Green  filter,  23,  29. 
Green  light,  13. 
Green  safelight,  41. 
Green  spots,  163. 
Grey  scale,  55. 
Grotthus-Draper  law,  179. 
Gum-bichromate  pigments,  in. 
Gum-bichromate  sensitizer,  113. 
Gurtner,  J.,  217. 

Half  wave-lengths,  187. 
Heliochromes,  fixing,  196. 
Heliochromes,  mounting,  197. 
Heliochromes,  viewing,  198. 
Heliochromic  spectra,  193. 
Heliochromy,  interference,  185. 
Helmholtz,  6. 

Herschel,  Sir  John  W.,  200. 
Hydrochinon  developer,  44. 
Hydrogen  peroxide,  182. 
Hydrogen  peroxide  etching,  88. 
Hiibl,  von,  122. 
Hunt,  Robert,  200. 
Hypersensitizing     autochromes, 
148. 

Ilford  plates,  20. 
Imbibition  process,  75. 
Iodide  mordant,  95. 
Infra-red,  186. 

Intensification,  screen-plate,  154 
Interference  heliochromy,  185. 
Isensee,  H.,  230. 
Isocyanin  dyes,  16. 
Ives,  H.  E.  193,  211. 

Joly,  J.,  136. 
Juxtaposed  colors,  136. 

Kinemacolor,  233. 
Kodachrome  bleacher,  227. 
Kodachrome  dyes,  228. 
Kodachrome  process,  226. 
Kopp,  R.,  202. 

Lanchester,  F.  M.,  212. 
Law  of  reflection,  187. 
Liesegang,  R.  E.,  88,  213. 


Lippmann,  G.,  185,  211. 
Lippmann  developer,  196. 
Lippmann  gelatine  emulsion,i9i. 
Lippmann  plate  holder,  194. 
Lippmann  plates,  218. 
Lippmann  process,  185. 
Liquid  filters,  25. 
Loops,  188. 

Lumiere,  121,  137,  168. 
Luminosity,  visual,  142. 

Magnesium  ribbon,  159. 
Making  filters,  29. 
McDonough,  J.  W.  136. 
Marking  negatives,  57. 
Mees,  C.  E.  K.,  50. 
Meister,  Lucius  &  Briining,  75. 
Mercuric  iodide  toning,  103. 
Mercury  mirror,  188. 
Metol-hydrochinon      developer, 

47,  150- 

Metoquinon,  151. 
Minus  green  filter,  54. 
Minus  colors,  24. 
Minus  blue,  25. 
Minus  red,  25. 
Minus  yellow,  25. 
Moelants,  L.,  212. 
Mordant,  copper,  99. 
Mordant,  iodide,  95. 
Mordant,  vanadium,  100. 
Mordanting  process,  95. 
Mounting  heliochromes,  197. 

Namias,  R.,  100. 
Negative,  character  of,  46. 
Negative  developers,  46. 
Negative  marking,  57. 
Niepce  de  St.  Victor,  200 
Nitrite  bath,  45. 
Nodes,  188. 
Novak,  R.,  146. 

Oiling  glass,  31. 
Optical  flats,  38. 
Oxidized  pyrogallol,  92. 

Paget  screen-plate,  137,  170. 
Panchromatic  film,  21. 


INDEX 


247 


Panchromatic  plates,  12,  20. 
Panchromatizing  dyes,  15. 
Paper  actinometer,  64. 
Paper  shrinkage,  81. 
Parallax,  232. 
Paramidophenol,  47. 
Perhydrol,  182. 
Permanganate  reverser,  151. 
Persistence  of  vision,  230. 
Photochromoscope,  125. 
Photomechanical  work,  38. 
Photomicrography,  159. 
Physical  development,  162. 
Physical  intensifier,  154. 
Pinatype  final  support,  80. 
Pinatype  prints,  correcting,  83. 
Pinatype  prints,  fixing,  83. 
Pinatype  print-plates,  76. 
Pinatype  process,  75. 
Pinatype  transparencies,  124. 
Plate-blocks,  218. 
Plates,  commercial,  19. 
Plates,  drying,  18. 
Plates,  panchromatic,  12,  20. 
Plates,  sensitive,  12. 
Plate  sensitiveness  curves,  142, 

220. 

Poitevin,  A.  L.,  201. 
Polyfolium  dialyticum,  223. 
Position  of  filter,  36,  143. 
Powrie,  J.  H.,  143. 
Practical  sensitiveness,  147. 
Print  meter,  63. 
Print-plates,  decolorizing,  80. 
Print-plates,  pinatype,  76. 
Printing  box,  169. 
Printing  colors,  79. 
Printing  gratings,  207. 
Printing  screen-plates,  168,  171. 
Printing  through  back,  120. 
Primary  colors,  6. 
Prismatic  dispersion,  212. 
Prussian  blue  toning,  103. 
Pyro-ammonia,  149. 
Pyrogallol,  oxidized,  92. 

Ratio  of  exposures,  55. 
Raydex  process,  71. 
Rayleigh,  Lord,  185. 


Raymond,  R.,  212. 
Red  filter,  23,  29. 
Reducer,  Farmer's  93. 
Reducer,  ferric  oxalate,  93. 
Reflection,  double,  27. 
Reflection,  law  of,  187. 
Reflector,  colored,  51. 
Refraction  process,  213. 
Register,  71. 

Registering  gum  prints,  115. 
Registration,  79. 
Relief  processes,  84,  127. 
Reliefs,  developed,  88. 
Reliefs,  etched,  88. 
Reliefs,  bichromated,  85. 
Rendall,  H.  E.,  53. 
Reversal  of  image,  151. 
Reversal  of  screen-plates,  141. 
Reverser,  bichromate,  151. 
Reverser,  permanganate,  151. 
Rheinberg,  J.,  213. 
Rodinal,  151. 
Room,  sensitizing,  19. 
Rulings  of  gratings,  207. 

Safelight,  green,  41. 
Scale  of  greys,  55. 
Screen-plates,  136. 
Screen-plate  action,  138. 
Screen-plate,  cutting,  177. 
Screen-plate,  combined,  140. 
Screen-plate  development,  148. 
Screen-plate  elements,  140. 
Screen-plate,  exposure  of,  146. 
Screen-plate  filters,  144. 
Screen-plate,  flashlight,  145. 
Screen-plate  printing,  168,  175. 
Screen-plate  reversal,  141. 
Screen-plate,  separate,  140. 
Screen-plate,  stereoscopic,  176. 
Second  development,  153. 
Seebeck,  J.  T.,  200. 
Seebeck  process,  200. 
Semi-dialyte  camera,  55,  223. 
Sensation,  three-color,  22. 
Sensitive  plates,  12. 
Sensitiveness,  plate,  142. 
Sensitizer,  carbon,  62. 
Sensitizing  by  bathing,  12. 


248 


INDEX 


Sensitizing  celluloid,  118. 
Sensitizing  film,  21. 
Sensitizing  room,  19. 
Separate  screen-plates,  140. 
Sharp-cutting  filters,  171. 
Shrinkage  of  paper,  81. 
Silver  bromide  emulsion,  119. 
Silver  laminae,  188. 
Silver  subchloride,  200. 
Simpson,  Wharton,  201. 
Size  of  filter,  27. 
Sliding  back,  38. 
Smith,  G.  A.,  217,  233. 
Sodium  nitrite,  45. 
Sodium  bisulphite,  96. 
Spectrum,  colors  of,  i. 
Standing  or  stationary  waves, 

188. 

Stereoscopic  screen-plates,  176. 
Stretching  of  paper,  no. 
Stripping  filters,  33. 
Stripping,  formaldehyde,  107. 
Stripping  plates,  105. 
Subtractive  cine  films,  234. 
Subtractive  printing  colors,  24. 
Subtractive  processes,  11,22,60. 
Superimposed  carbons,  60,  70. 
Support,  final,  69. 
Support,  temporary,  61. 

Tacky  glass,  117. 
Tartar  emetic,  184. 
Taupenot  process,  189. 
Temperature  of  developer,  48. 
Temporary  support,  61,  66. 
Thickness  of  filters,  52. 
Thiosinamin,  182. 
Thorp,  T.,  210. 
Three-color  gum  prints,  no. 
Three-color  sensations,  22. 
Three-color  slides,  117. 
Toning  processes,  95. 


Transmissions  of  filters,  95. 
Traube,  A.,  95,  99. 
Tri-color  green  filter,  54. 
Tri-pack,  217,  222. 
Turmeric,  183. 
Two-color  processes,  217,  220. 

Ultramarine,  112. 
Ultra-violet,  186. 

Valenta,  E.,  190. 
Vanadium  mordant,  99. 
Vanadium  oxalate,  101. 
Vanadium  sulphate,  101. 
Varnish,  celluloid,  82. 
Varnishing  screen-plates,  157. 
Velocity  of  development,  40. 
Viewing  diffraction  pictures,  210. 
Viewing  frame,  167. 
Viewing  heliochroines,  198. 
Vision,  persistence  of,  230. 
Visual  luminosity,  142. 

Warnerke,  L.,  92. 

Wave  crest,  187. 

Wave-lengths,  186. 

Wave  troughs,  187. 

Waves,  standing,  188. 

Waves,  stationary,  188. 

Waxing  solution,  66. 

Weights  and  measures,  235. 

Wiener,  O.,  185. 

Wood,  R.  W.,  205. 

Wratten  &  Wainwright  plates, 

20. 
Wratten  &  Wainwright  filters, 

54,  173,  219,  221. 

Young,  Thos.,  6. 
Zenker,  W.,  185. 


WRATTEN 
LIGHT  FILTERS 

for 

Photographic  Technical 
and  Scientific  Work 

Over  IOO  Varieties 

Special  sets  of  filters  suitable  for  experi- 
mental work  in  orthochromatic  photo- 
graphy, contrast  photography  of  colored 
objects,  color  photography  and  color 
cinematography,  photomicrography, 
spectroscopy  and  photometry. 


Send  J or  our  Condensed  List  of 
Filters — free  on  application 

Eastman  Kodak  Company 

Rochester,  N.  Y. 


Your  Success  in  Photography 


•[71  VERY  reader  of  this  volume  is  seriously  interested  in  tl 


uccess  of  his  photographic 
fforts.     The  secret  of  good  results  is  information,  backed  by  experience.     Informa 


must  be  up-to-date,  authentic,  and  to  be  valuable  the  useless  facts  must  be 
weeded  out  from  the  practical  "meaty"  matter,  and  the  net  result  presented  to  the  reader. 
This  is  what  the  editors  are  doing,  in  our  monthly  magazine  AMERICAN  PHOTOG- 
RAPHY. For  more  than  thirty  years  this  magazine  lias  served  the  American  photographic 
public,  and  endeavored  to  be  all  that  its  name  implies  —  the  standard  American  photo- 
graphic magazine.  It  covers  the  whole  field  of  photography,  for  amateur,  professional  and 
commercial  workers,  publishing  each  month  forceful  articles  on  the  best  current  practice 
and  latest  advances  in  each  of  these  classifications.  The  monthly  departments  include 
several  monthly  competitions,  criticism  of  pictures,  questions  answered,  notes  for  beginners, 
notes  and  news  of  clubs,  book  reviews,  a  comprehensive  review  of  all  that  is  new  in  photog- 
raphy by-Professor  Wall,  etc.  In  short,  we  publish  a  readers'  magazine,  and  in  addition 
place  our  editorial  staff  at  the  service  of  our  friends,  to  help  them  with  perplexing  problems. 
This  means  you! 

Does  a  magazine  published  along  such  lines  meet  your  ideas  of  good  service?  We  think 
it  does,  for  we  try  to  put  ourselves  in  our  readers'  position  when  we  consider  a  change  in  the 
makeup  of  the  magazine.  Join  our  steadily  increasing  circle  of  readers  and  friends.  The 
subscription  price  is  but  $2.50  per  year,  including  personal  editorial  help  when  you  need  it. 
Send  your  subscription  today  and  look  forward  to  twelve  numbers  of  the  best  photographic 
literature  that  you  have  ever  read. 

American    Photographic    Publishing    Co. 

428  NEWBURY  STREET,  BOSTON  17,  MASS. 


Optics  for  Photographers 

Translated  from  the  original  of 

HANS  HARTING,  Ph.D. 

By 

FRANK  R.  FRAPRIE,  S.M..F.R.P.S. 
T^HE  writer  of  this  book  starts  witi, 
A  the  fundamental  laws  of  the  propa- 
gation of  light,  and  carefully  and  logi- 
cajly  carries  the  reader  through  the 
principles  of  geometrical  optics  to  a 
complete  explanation  of  the  action  of 
all  types  of  photographic  lenses,  and  a 
description  of  their  qualities  and  de- 
fects. Only  the  simplest  mathematics 
is  used,  and  this  sparingly.  The  book 
is  brilliantly  worked  out  and  is  indis- 
pensable in  the  photographic  library, 
being  the  only  modern  and  compre- 
hensive work  on  the  subject  in  English. 
The  author  is  the  calculator  and  in- 
ventor of  a  well-known  series  of  high 
grade  anastigmat  lenses;  he  has  the 
happy  facility  of  expressing  himself  in 
such  clear,  simple  language  that  no 
one  will  have  the  least  difficulty  in 
understanding  his  exposition  of  the 
subject.  Bound  in  Red  Cloth,  $2.50 
AMERICAN  PHOTOGRAPHIC 

PUBLISHING   CO. 
428  Newbury  St.        Boston  17,  Mass. 


CHEMISTRY  FOR 
PHOTOGRAPHERS 

By  WILLIAM  R.  FLINT,  Ph.D. 
New  and  Revised  Edition 

part  played  by  chemistry  in 
photography  is  so  important  that  a 
knowledge  of  photographic  chemistry  is 
a  big  help  to  the  photographer.  One 
does  not  need  to  be  a  chemist  to  under- 
stand the  valuable  material  the  author 
has  placed  in  this  book.  It  explains  the 
types  of  chemical  actions  that  have  to 
do  with  photography,  makes  clear  the 
application  of  each  to  some  photographic 
process,  and  gives  the  reader  such  a 
clear  idea  of  what  he  is  doing  chemically, 
while  he  works  photographically,  that 
he  cannot  fail  to  make  systematic 
progress. 

Bound  in  Red  Cloth,  $2.50 

AMERICAN    PHOTOGRAPHIC 

PUBLISHING    CO. 
428  Newbury  St.       Boston  17,  Mass. 


SOEPZ  Lenses 

Ideal  for  Color  Photography 

DOGMARF:4.5.  DAGORF:6.8. 

BECAUSE  of  their   high  color  correction,  both 
the   Goerz  Dogmar  F:  4.  5   and  Dagor  F:6.8 
render  equally  sharp  all  details  in  colored  objects 
to  be  photographed.     The  images  are  exceptionally 
brilliant  and  crisp. 

For  autochrome  work,  the  Dogmar  is  especially 
suited,  because  of  its  high  speed.  It  is  free  from 
coma  and  flare. 

The  finest  color  corrected  lens  for  color  separation 
work  in  photo-engraving  is  the  Goerz  Artar  F:9 
and  F:  12.  5.  It  is  perfectly  corrected  for  spherical 
and  zonal  aberration,  astigmatism;  coma  and  flare 
and  produces  equal  size  negatives. 

Ask  your  dealer  about  Goerz  lenses 
and  the  results  they  give,  or  write 
us  for  full  information. 

C.    P.    GOERZ    AMERICAN    OPTICAL    CO. 

319c    EAST    34TH    STREET  NEW    YORK    CITY 


PRACTICAL  SUPPLIES 

FOR    COLOR    PHOTOGRAPHY 

Paget  Color  Process 

For  the  first  time  in  several  years,  we  are  in  a  position  to 
supply:  Viewing  Screens,  Taking  Screens,  Panchromatic 
Negative  Plates  and  Transparency  Plates,  for  the  PAGET 
COLOR  PROCESS. 

Descriptive  literature  upon  request. 

Lifa  Light  Filters 

We  have  been  appointed  exclusive  agents  for  the  United 
States  and  its  territories,  for  the  famous  LIFA  LIGHT 
FILTERS,  made  by  the  Lifa  Light  Filter  Works  of 
Augsburg,  Germany. 

Included  in  the  LIFA  line  are  three  and  four  color 
separation  filters,  adapted  for  all  Orthochromatic  and  Pan- 
chromatic plates. 

Filters  for  direct  photography  of  colors,  on  Agfa  and 
Autochrom  plates. 

Filters  for  scientific  purposes,  including  those  for  selec- 
tive contrasts,  monochromatic  and  micrography,  dark  room 
lights,  photographic  prints  and  for  the  correction  of  promi- 
nent screen  plates. 

LIFA  graduated-  filters  for  sky,  cloud  and  landscape 
photography. 

A  complete  text  book  on  light  filters  and  their  use,  now  in 
preparation.  Summary  of  contents  and  other  interesting 
data  forwarded  upon  request. 

HERBERT  &   HUESGEN   CO. 

18  E.  42ND-ST.,  NEW  YORK  CITY 
Photographic,  Scientific,  Wireless  and  Motion  Picture  Apparatus  and  Supplies 


COLOR  PHOTOGRAPHY 

A  simple  process  for  making  Photo- 
graphic Transparencies  and 
Lantern  Slides  in  natural  colors. 

The  negatives  are  obtained  by  single 
exposures  in  the  camera,  after  which  any 
number  of  transparencies  (positives)  can 
be  made  from  the  negative.  Simple  photo- 
graphic methods  are  employed  from  start 
to  finish. 

The  materials  essential  to  the  process  are: 
Taking  Screen,  Compensating  Filter,  Pan- 
chromatic Negative  Plates,  Transparency 
Plates,  Viewing  Screens  —  some  of  which 
are  used  over  and  over  again.  All  must  be 
of  PAGET  manufacture,  however,  as  all  the 
materials  are  specially  made  for  the  process. 

Anyone  who  uses  a  plate  camera  can 
take  color  photographs  by  the  Paget  process. 

Write  for  working  instructions  and 
particulars  and  prices  of  outfits. 

AMALGAMATED    PHOTOGRAPHIC 
MANUFACTURERS,    LIMITED 


114  EAST  28xH  ST. 
NEW  YORK 


HEAD  OFFICE,  3  SOHO  SQ. 
LONDON,  ENGLAND 


Wollensak  Velostigmats 


PRECISION    ANASTIGMATS 

FOR 

PRECISION     PURPOSES 


Wollensak    Optical    Co. 

ROCHESTER,    N.Y.,    U.S.A. 
Ftlostitmat      V  i  t  a  x        and       V  e  r  i  t  o 


LUMIERE 

Autochrome  Plates 

FOR  DIRECT  COLOR  PHOTOGRAPHY 

The  process  is  very  simple.  Any  amateur  with  a  plate 
camera  and  an  autochrome  lens  filter  may  obtain  with 
simple  development,  within  15  minutes,  a  finished  picture 
in  color  absolutely  true  to  nature. 

Booklet  on  request 

R.  J.  FITZSIMMONS 

75  Fifth  Avenue  New  York  City 


SPECIAL  RAPID 

P^NCHR  0  M^TIC 
PLATES 

Are     Sensitive     to     ALL     COLORS 

The  cleanest  and  most  rapid  of  ALL  Panchromatic  Plates. 
They  can  be  used  for  instantaneous  photography  even  with  a 
deep  correcting  filter  in  position.  They  give  a  correct  render- 
ing in  monochrome  of  the  actual  visual  color  values. 
The  ILFORD  Rapid  Process  Panchromatic  Plates  are  equally 
color-sensitive  but  of  a  slower  speed,  and  may  be  used  where 
greater  contrast  is  required. 

From  all  Dealers 

"Panchromatism,"  the  illustrated  booklet  on  the  use  of  the  Ilford 
Panchromatic  Plates,  post  free  9d.,  or  4  International  coupons. 


ILFORD 
Limited 

ILFORD,  LONDON,  England 


Books  on  Photography 


Optics  for  Photographers,  by  Hans  Harting,  Ph.D.  Translated 
by  Frank  R.  Fraprie,  S.M.,  F.R.P.S.  232  pages.  Cloth,  $2.50. 

Chemistry  for  Photographers,  by  William  R.  Flint.  2nd  edition. 
218  pages.  Cloth,  $2.50. 

Pictorial  Composition  in  Photography,  by  Arthur  Hammond. 
234  pages,  49  illustrations.  Cloth,  $3.50. 

Photo-Engraving  Primer,  by  Stephen  H.  Horgan.     Cloth,  $1.50. 

Cash  from  Your  Camera.  Edited  by  Frank  R.  Fraprie,  S.M., 
F.R.P.S.  Paper,  $1.00. 

Pictorial  Landscape  Photography,  by  the  Photo  Pictorialists  of 
Buffalo.  252  pages,  55  illustrations.  Cloth,  $3.50. 

Photographic  Amusements,  by  Walter  E.  Woodbury.  gth  edition. 
128  pages,  100  illustrations.  Cloth,  $1.50. 

Practical  Color  Photography,  by  E.  J.  Wall,  F.C.S.,  F.R.P.S. 
Cloth,  $3.00. 

PRACTICAL   PHOTOGRAPHY  SERIES 

Edited  by  Frank  R.  Fraprie,  S.M.,  F.R.P.S. 

Editor  of  American  Photography 

1.  The  Secret  of  Exposure. 

2.  Beginners'  Troubles. 

3.  How  to  Choose  and  Use  a  Lens. 

4.  How  to  Make  Prints  in  Color. 

5.  How  to  Make  Enlargements. 

6.  How  to  Make  Portraits. 

7.  How  to  Make  Lantern  Slides. 

8.  The  Elements  of  Photography. 

9.  Practical  Retouching. 

Each  volume  sold  separately.     Cloth,  $1.00;  paper,  50  cents. 

American  Photography  Exposure  Tables,  loist  thousand.  Cloth, 
35  cents. 

Thermo  Development  Chart.     25  cents. 

American  Photography,  a  monthly  magazine,  representing  all  that 
its  name  implies.  25  cents  a  copy.  $2.50  a  year. 


PUBLISHED   BY 


American    Photographic   Publishing   Co. 

428  Newbury  St.,  Boston  17,  Massachusetts 


A 
UNIYERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 
This  book  is  DUE  on  the  last  date  stamped  below. 

J? 

lUfU  W-UWf 

JUM25198Q 

i 

»•* 

S 

E  APR  i  HS83 

1 

% 

e: 

^fK^ 

^** 

1 

% 

1  5^ 

f 

j 

i 

-X585            45E--  --K            . 

?-  -=^.  $  % 

i  \f^j  s  §  *YT^J  s  i  ^  """"tN  s 

i  s 


^l-LIBRARY^  A\\El)NIVERS/A         . 

< 


^t-llBRARY-Qr 


